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614 lines
15 KiB
C
614 lines
15 KiB
C
/*
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WIP
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Simple realtime 3D software rasterization library. It is fast, focused on
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resource-limited computers, located in a single C header file, with no
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dependencies, using only integer arithmetic.
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author: Miloslav Ciz
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license: CC0 1.0
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--------------------
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COORDINATE SYSTEMS:
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In 3D space, a left-handed coord. system is used. One spatial unit is split
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into S3L_FRACTIONS_PER_UNIT fractions.
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y ^
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| _
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| /| z
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| /
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| /
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[0,0,0]-------> x
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Untransformed camera is placed at [0,0,0], looking forward along +z axis. The
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projection plane is centered at [0,0,0], stretrinch from
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-S3L_FRACTIONS_PER_UNIT to S3L_FRACTIONS_PER_UNIT horizontally (x),
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vertical size (y) depends on the camera aspect ratio. Camera FOV is defined
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by focal length.
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y ^
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____|_/__
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| |/ |
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-----[0,0,0]-|-----> x
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|____|____|
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Coordinates of pixels on screen start typically at the top left.
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*/
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#ifndef S3L_H
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#define S3L_H
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#include <stdint.h>
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typedef int16_t S3L_Unit; /**< Units of measurement in 3D space. There is
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S3L_FRACTIONS_PER_UNIT in one spatial unit.
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By dividing the unit into fractions we
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effectively achieve fixed point arithmetic.
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The number of fractions is a constant that
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serves as 1.0 in floating point arithmetic
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(normalization etc.). */
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#define S3L_FRACTIONS_PER_UNIT 1024
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typedef int16_t S3L_ScreenCoord;
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typedef uint16_t S3L_Index;
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typedef struct
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{
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S3L_Unit x;
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S3L_Unit y;
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S3L_Unit z;
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} S3L_Vec3;
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static inline void S3L_initVec3(S3L_Vec3 *v)
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{
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v->x = 0; v->y = 0; v->z = 0;
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}
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typedef struct
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{
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S3L_Vec3 offset;
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S3L_Vec3 rotation;
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S3L_Vec3 scale;
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} S3L_Transform3D;
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static inline void S3L_initTransoform3D(S3L_Transform3D *t)
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{
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S3L_initVec3(&(t->offset));
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S3L_initVec3(&(t->rotation));
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t->scale.x = S3L_FRACTIONS_PER_UNIT;
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t->scale.y = S3L_FRACTIONS_PER_UNIT;
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t->scale.z = S3L_FRACTIONS_PER_UNIT;
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}
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typedef struct
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{
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uint16_t resolutionX;
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uint16_t resolutionY;
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S3L_Unit focalLength; ///< Defines the field of view (FOV).
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S3L_Transform3D transform;
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} S3L_Camera;
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static inline void S3L_initCamera(S3L_Camera *c)
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{
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c->resolutionX = 128;
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c->resolutionY = 64;
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c->focalLength = S3L_FRACTIONS_PER_UNIT;
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S3L_initTransoform3D(&(c->transform));
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}
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typedef struct
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{
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S3L_ScreenCoord x; ///< Screen X coordinate.
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S3L_ScreenCoord y; ///< Screen Y coordinate.
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S3L_Unit barycentric0; /**< Barycentric coord 0 (corresponds to 1st vertex).
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Together with 1 and 2 coords these serve to
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locate the pixel on a triangle and interpolate
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values between it's three points. The sum of the
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three coordinates will always be exactly
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S3L_FRACTIONS_PER_UNIT. */
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S3L_Unit barycentric1; ///< Baryc. coord 1 (corresponds to 2nd vertex).
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S3L_Unit barycentric2; ///< Baryc. coord 2 (corresponds to 3rd vertex).
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S3L_Index triangleID;
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} S3L_PixelInfo;
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static inline void S3L_initPixelInfo(S3L_PixelInfo *p)
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{
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p->x = 0;
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p->y = 0;
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p->barycentric0 = S3L_FRACTIONS_PER_UNIT;
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p->barycentric1 = 0;
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p->barycentric2 = 0;
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p->triangleID = 0;
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}
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#define S3L_BACKFACE_CULLING_NONE 0
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#define S3L_BACKFACE_CULLING_CW 1
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#define S3L_BACKFACE_CULLING_CCW 2
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#define S3L_MODE_TRIANGLES 0
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#define S3L_MODE_LINES 1
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#define S3L_MODE_POINTS 2
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typedef struct
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{
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int backfaceCulling;
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int mode;
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} S3L_DrawConfig;
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void S3L_PIXEL_FUNCTION(S3L_PixelInfo *pixel); // forward decl
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typedef struct
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{
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int16_t steps;
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int16_t err;
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S3L_ScreenCoord x;
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S3L_ScreenCoord y;
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int16_t *majorCoord;
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int16_t *minorCoord;
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int16_t majorIncrement;
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int16_t minorIncrement;
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int16_t majorDiff;
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int16_t minorDiff;
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} S3L_BresenhamState; ///< State of drawing a line with Bresenham algorithm.
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/**
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Returns a value interpolated between the three triangle vertices based on
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barycentric coordinates.
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*/
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static inline S3L_Unit S3L_interpolateBarycentric(
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S3L_Unit value0, S3L_Unit value1, S3L_Unit value2,
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S3L_Unit barycentric0, S3L_Unit barycentric1, S3L_Unit barycentric2)
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{
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return
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(
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(value0 * barycentric0) +
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(value1 * barycentric1) +
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(value2 * barycentric2)
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) / S3L_FRACTIONS_PER_UNIT;
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}
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// general helper functions
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static inline int16_t S3L_abs(int16_t value)
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{
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return value >= 0 ? value : -1 * value;
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}
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static inline int16_t S3L_min(int16_t v1, int16_t v2)
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{
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return v1 >= v2 ? v2 : v1;
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}
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static inline int16_t S3L_max(int16_t v1, int16_t v2)
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{
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return v1 >= v2 ? v1 : v2;
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}
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static inline S3L_Unit S3L_wrap(S3L_Unit value, S3L_Unit mod)
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{
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return value >= 0 ? (value % mod) : (mod + (value % mod) - 1);
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}
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static inline S3L_Unit S3L_nonZero(S3L_Unit value)
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{
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return value != 0 ? value : 1;
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}
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/**
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Interpolated between two values, v1 and v2, in the same ratio as t is to
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tMax. Does NOT prevent zero division.
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*/
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static inline int16_t S3L_interpolate(int16_t v1, int16_t v2, int16_t t,
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int16_t tMax)
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{
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return v1 + ((v2 - v1) * t) / tMax;
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}
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/**
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Same as S3L_interpolate but with v1 = 0. Should be faster.
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*/
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static inline int16_t S3L_interpolateFrom0(int16_t v2, int16_t t, int16_t tMax)
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{
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return (v2 * t) / tMax;
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}
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void S3L_bresenhamInit(S3L_BresenhamState *state, int16_t x0, int16_t y0,
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int16_t x1, int16_t y1)
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{
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int16_t dx = x1 - x0;
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int16_t dy = y1 - y0;
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int16_t absDx = S3L_abs(dx);
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int16_t absDy = S3L_abs(dy);
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if (absDx >= absDy)
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{
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state->majorCoord = &(state->x);
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state->minorCoord = &(state->y);
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state->minorDiff = 2 * absDy;
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state->majorDiff = 2 * absDx;
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state->err = 2 * dy - dx;
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state->majorIncrement = dx >= 0 ? 1 : -1;
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state->minorIncrement = dy >= 0 ? 1 : -1;
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state->steps = absDx;
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}
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else
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{
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state->majorCoord = &(state->y);
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state->minorCoord = &(state->x);
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state->minorDiff = 2 * absDx;
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state->majorDiff = 2 * absDy;
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state->err = 2 * dx - dy;
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state->majorIncrement = dy >= 0 ? 1 : -1;
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state->minorIncrement = dx >= 0 ? 1 : -1;
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state->steps = absDy;
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}
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state->x = x0;
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state->y = y0;
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}
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int S3L_bresenhamStep(S3L_BresenhamState *state)
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{
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state->steps--;
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(*state->majorCoord) += state->majorIncrement;
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if (state->err > 0)
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{
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(*state->minorCoord) += state->minorIncrement;
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state->err -= state->majorDiff;
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}
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state->err += state->minorDiff;
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return state->steps >= 0;
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}
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void S3L_drawTriangle(
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S3L_ScreenCoord x0, S3L_ScreenCoord y0,
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S3L_ScreenCoord x1, S3L_ScreenCoord y1,
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S3L_ScreenCoord x2, S3L_ScreenCoord y2,
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S3L_DrawConfig config)
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{
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if (config.backfaceCulling != S3L_BACKFACE_CULLING_NONE)
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{
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int cw = // matrix determinant
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x0 * y1 + y0 * x2 + x1 * y2 - y1 * x2 - y0 * x1 - x0 * y2 > 0;
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if ((config.backfaceCulling == S3L_BACKFACE_CULLING_CW && !cw) ||
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(config.backfaceCulling == S3L_BACKFACE_CULLING_CCW && cw))
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return;
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}
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S3L_PixelInfo p;
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S3L_initPixelInfo(&p);
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// point mode
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if (config.mode == S3L_MODE_POINTS)
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{
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p.x = x0; p.y = y0; p.barycentric0 = S3L_FRACTIONS_PER_UNIT;
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p.barycentric1 = 0; p.barycentric2 = 0;
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S3L_PIXEL_FUNCTION(&p);
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p.x = x1; p.y = y1; p.barycentric0 = 0;
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p.barycentric1 = S3L_FRACTIONS_PER_UNIT; p.barycentric2 = 0;
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S3L_PIXEL_FUNCTION(&p);
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p.x = x2; p.y = y2; p.barycentric0 = 0;
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p.barycentric1 = 0; p.barycentric2 = S3L_FRACTIONS_PER_UNIT;
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S3L_PIXEL_FUNCTION(&p);
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return;
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}
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// line mode
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if (config.mode == S3L_MODE_LINES)
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{
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S3L_BresenhamState line;
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S3L_Unit lineLen;
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#define drawLine(p1,p2)\
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S3L_bresenhamInit(&line,x##p1,y##p1,x##p2,y##p2);\
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p.barycentric0 = 0;\
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p.barycentric1 = 0;\
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p.barycentric2 = 0;\
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lineLen = S3L_nonZero(line.steps);\
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do\
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{\
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p.x = line.x; p.y = line.y;\
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p.barycentric##p1 = S3L_interpolateFrom0(\
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S3L_FRACTIONS_PER_UNIT,line.steps,lineLen); \
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p.barycentric##p2 = S3L_FRACTIONS_PER_UNIT - p.barycentric##p1;\
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S3L_PIXEL_FUNCTION(&p);\
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} while (S3L_bresenhamStep(&line));
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drawLine(0,1)
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drawLine(2,0)
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drawLine(1,2)
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#undef drawLine
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return;
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}
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// triangle mode
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S3L_ScreenCoord
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tPointX, tPointY, // top triangle point coords
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lPointX, lPointY, // left triangle point coords
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rPointX, rPointY; // right triangle point coords
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S3L_Unit *barycentric0; // bar. coord that gets higher from L to R
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S3L_Unit *barycentric1; // bar. coord that gets higher from R to L
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S3L_Unit *barycentric2; // bar. coord that gets higher from bottom up
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// Sort the points.
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#define handleLR(t,a,b)\
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int16_t aDx = x##a - x##t;\
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int16_t bDx = x##b - x##t;\
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int16_t aDy = S3L_nonZero(y##a - y##t);\
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int16_t bDy = S3L_nonZero(y##b - y##t);\
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if ((aDx << 4) / aDy < (bDx << 4) / bDy)\
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/*if (x##a <= x##b)*/\
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{\
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lPointX = x##a; lPointY = y##a;\
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rPointX = x##b; rPointY = y##b;\
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barycentric0 = &p.barycentric##b;\
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barycentric1 = &p.barycentric##a;\
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}\
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else\
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{\
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lPointX = x##b; lPointY = y##b;\
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rPointX = x##a; rPointY = y##a;\
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barycentric0 = &p.barycentric##a;\
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barycentric1 = &p.barycentric##b;\
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}
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if (y0 <= y1)
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{
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if (y0 <= y2)
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{
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tPointX = x0;
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tPointY = y0;
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barycentric2 = &p.barycentric0;
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handleLR(0,1,2)
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}
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else
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{
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tPointX = x2;
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tPointY = y2;
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barycentric2 = &p.barycentric2;
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handleLR(2,0,1)
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}
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}
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else
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{
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if (y1 <= y2)
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{
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tPointX = x1;
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tPointY = y1;
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barycentric2 = &p.barycentric1;
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handleLR(1,0,2)
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}
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else
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{
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tPointX = x2;
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tPointY = y2;
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barycentric2 = &p.barycentric2;
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handleLR(2,0,1)
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}
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}
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// Now draw the triangle line by line.
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#undef handleLR
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S3L_ScreenCoord splitY; // Y at which one side (L or R) changes
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S3L_ScreenCoord endY; // bottom Y of the whole triangle
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int splitOnLeft; // whether split happens on L or R
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if (rPointY <= lPointY)
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{
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splitY = rPointY;
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splitOnLeft = 0;
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endY = lPointY;
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}
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else
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{
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splitY = lPointY;
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splitOnLeft = 1;
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endY = rPointY;
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}
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S3L_ScreenCoord currentY = tPointY;
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/* We'll be using a slight modification of Bresenham line algorithm (a one
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that draws a _non-continous_ line). */
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int16_t
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/* triangle side:
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left right */
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lX, rX, // current x position
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lDx, rDx, // dx (end point - start point)
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lDy, rDy, // dy (end point - start point)
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lInc, rInc, // direction in which to increment (1 or -1)
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lErr, rErr, // current error (Bresenham)
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lErrAdd, rErrAdd, // error value to add in each Bresenham cycle
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lErrSub, rErrSub; // error value to substract when moving in x direction
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S3L_Unit
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lSideUnitStep, rSideUnitStep,
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lSideUnitPos, rSideUnitPos;
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int16_t helperDxAbs;
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#define initSide(v,p1,p2, down)\
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v##X = p1##PointX;\
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v##Dx = p2##PointX - p1##PointX;\
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v##Dy = p2##PointY - p1##PointY;\
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v##SideUnitStep = S3L_FRACTIONS_PER_UNIT / (v##Dy != 0 ? v##Dy : 1);\
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v##SideUnitPos = 0;\
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if (!down)\
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{\
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v##SideUnitPos = S3L_FRACTIONS_PER_UNIT;\
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v##SideUnitStep *= -1;\
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}\
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helperDxAbs = S3L_abs(v##Dx);\
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v##Inc = v##Dx >= 0 ? 1 : -1;\
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v##Err = 2 * helperDxAbs - v##Dy;\
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v##ErrAdd = 2 * helperDxAbs;\
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v##ErrSub = 2 * v##Dy;\
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v##ErrSub = v##ErrSub != 0 ? v##ErrSub : 1; /* don't allow 0, could lead
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to an infinite substracting
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loop */
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#define stepSide(s)\
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while (s##Err > 0)\
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{\
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s##X += s##Inc;\
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s##Err -= s##ErrSub;\
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}\
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s##Err += s##ErrAdd;
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initSide(r,t,r,1)
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initSide(l,t,l,1)
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while (currentY <= endY)
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{
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if (currentY == splitY)
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{
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if (splitOnLeft)
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{
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initSide(l,l,r,0);
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S3L_Unit *tmp = barycentric0;
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barycentric0 = barycentric2;
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barycentric2 = tmp;
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rSideUnitPos = S3L_FRACTIONS_PER_UNIT - rSideUnitPos;
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rSideUnitStep *= -1;
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}
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else
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{
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initSide(r,r,l,0);
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S3L_Unit *tmp = barycentric1;
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barycentric1 = barycentric2;
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barycentric2 = tmp;
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lSideUnitPos = S3L_FRACTIONS_PER_UNIT - lSideUnitPos;
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lSideUnitStep *= -1;
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}
|
|
}
|
|
|
|
p.y = currentY;
|
|
|
|
// draw the line
|
|
|
|
S3L_Unit tMax = rX - lX;
|
|
tMax = tMax != 0 ? tMax : 1; // prevent division by zero
|
|
|
|
S3L_Unit t1 = 0;
|
|
S3L_Unit t2 = tMax;
|
|
|
|
for (S3L_ScreenCoord x = lX; x <= rX; ++x)
|
|
{
|
|
*barycentric0 = S3L_interpolateFrom0(rSideUnitPos,t1,tMax);
|
|
*barycentric1 = S3L_interpolateFrom0(lSideUnitPos,t2,tMax);
|
|
*barycentric2 = S3L_FRACTIONS_PER_UNIT - *barycentric0 - *barycentric1;
|
|
|
|
p.x = x;
|
|
S3L_PIXEL_FUNCTION(&p);
|
|
|
|
++t1;
|
|
--t2;
|
|
}
|
|
|
|
stepSide(r)
|
|
stepSide(l)
|
|
|
|
lSideUnitPos += lSideUnitStep;
|
|
rSideUnitPos += rSideUnitStep;
|
|
|
|
++currentY;
|
|
}
|
|
|
|
#undef initSide
|
|
#undef stepSide
|
|
}
|
|
|
|
static inline void S3L_mapWorldToCamera(S3L_Vec3 point,
|
|
S3L_Transform3D *cameraTransform, S3L_Vec3 *newPoint)
|
|
{
|
|
newPoint->x = point.x - cameraTransform->offset.x;
|
|
newPoint->y = point.y - cameraTransform->offset.y;
|
|
newPoint->z = point.z - cameraTransform->offset.z;
|
|
}
|
|
|
|
static inline void S3L_mapCameraToScreen(S3L_Vec3 point, S3L_Camera *camera,
|
|
S3L_ScreenCoord *screenX, S3L_ScreenCoord *screenY)
|
|
{
|
|
uint16_t halfW = camera->resolutionX >> 1; // TODO: precompute earlier?
|
|
uint16_t halfH = camera->resolutionY >> 1;
|
|
|
|
*screenX = halfW + (point.x * halfW) / point.z;
|
|
*screenY = halfH - (point.y * halfW) / point.z;
|
|
// ^ S3L_FRACTIONS_PER_UNIT cancel out
|
|
}
|
|
|
|
void S3L_drawModel(
|
|
const S3L_Unit coords[],
|
|
const S3L_Index triangleVertexIndices[],
|
|
uint16_t triangleCount,
|
|
S3L_Camera camera,
|
|
S3L_DrawConfig config)
|
|
{
|
|
S3L_Index triangleIndex = 0;
|
|
S3L_Index coordIndex = 0;
|
|
|
|
while (triangleIndex < triangleCount)
|
|
{
|
|
S3L_ScreenCoord sX0, sY0, sX1, sY1, sX2, sY2;
|
|
S3L_Vec3 point, point2;
|
|
S3L_Unit indexIndex;
|
|
|
|
#define mapCoords(n)\
|
|
indexIndex = triangleVertexIndices[coordIndex] * 3;\
|
|
point.x = coords[indexIndex];\
|
|
++indexIndex; /* TODO: put into square brackets? */\
|
|
point.y = coords[indexIndex];\
|
|
++indexIndex;\
|
|
point.z = coords[indexIndex];\
|
|
++coordIndex;\
|
|
S3L_mapWorldToCamera(point,&camera.transform,&point2);\
|
|
S3L_mapCameraToScreen(point2,&camera,&sX##n,&sY##n);
|
|
|
|
mapCoords(0)
|
|
mapCoords(1)
|
|
mapCoords(2)
|
|
|
|
S3L_drawTriangle(sX0,sY0,sX1,sY1,sX2,sY2,config);
|
|
|
|
++triangleIndex;
|
|
}
|
|
}
|
|
|
|
#endif
|