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https://git.coom.tech/drummyfish/raycastlib.git
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138 lines
2.7 KiB
C
138 lines
2.7 KiB
C
#include <stdint.h>
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#include <stdio.h>
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/**
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author: Miloslav "drummyfish" Ciz
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license: CC0
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- Game field's bottom left corner is at [0,0].
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- X axis goes right.
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- Y axis goes up.
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- Each game square is UNITS_PER_SQUARE * UNITS_PER_SQUARE.
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*/
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#define UNITS_PER_SQUARE 1024
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typedef int64_t Unit; /**< Smallest spatial unit, there is UNITS_PER_SQUARE
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units in a square's length. */
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/// Position in 2D space.
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typedef struct
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{
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Unit y;
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Unit x;
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} Vector2D;
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typedef struct
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{
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Vector2D start;
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Vector2D direction;
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} Ray;
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//=============================================================================
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// privates
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#define logVector2D(v) printf("[%d,%d]\n",v.x,v.y)
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#define logRay(r) printf("{\n");\
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logVector2D(r.start);\
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logVector2D(r.direction);\
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printf("}\n");
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int8_t pointIsLeftOfRay(Vector2D point, Ray ray)
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{
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int dX = point.x - ray.start.x;
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int dY = point.y - ray.start.y;
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return (ray.direction.x * dY - ray.direction.y * dX) > 0;
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// ^ Z component of cross-product
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}
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/**
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*/
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void castRaySquare(Ray globalRay, Vector2D *nextCellOffset,
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Vector2D *collisionPointOffset)
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{
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globalRay.start.x %= UNITS_PER_SQUARE;
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globalRay.start.y %= UNITS_PER_SQUARE;
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nextCellOffset->x = 0;
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nextCellOffset->y = 0;
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Ray criticalLine = globalRay;
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#define helper(c1,c2,n)\
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{\
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nextCellOffset->c1 = n;\
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collisionPointOffset->c1 = criticalLine.start.c1 - globalRay.start.c1;\
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collisionPointOffset->c2 =\
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(collisionPointOffset->c1 * globalRay.direction.c2) /\
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(globalRay.direction.c1 == 0 ? 1 : globalRay.direction.c1);\
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}
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#define helper2(n1,n2,c)\
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if (pointIsLeftOfRay(globalRay.start,criticalLine) == c)\
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helper(y,x,n1)\
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else\
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helper(x,y,n2)
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if (globalRay.direction.x > 0)
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{
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criticalLine.start.x = UNITS_PER_SQUARE - 1;
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if (globalRay.direction.y > 0)
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{
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// top right
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criticalLine.start.y = UNITS_PER_SQUARE - 1;
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helper2(1,1,1)
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}
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else
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{
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// bottom right
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criticalLine.start.y = 0;
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helper2(-1,1,0)
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}
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}
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else
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{
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criticalLine.start.x = 0;
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if (globalRay.direction.y > 0)
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{
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// top left
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criticalLine.start.y = UNITS_PER_SQUARE - 1;
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helper2(1,-1,0)
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}
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else
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{
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// bottom left
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criticalLine.start.y = 0;
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helper2(-1,-1,1)
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}
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}
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#undef helper2
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#undef helper
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}
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int main()
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{
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Ray r;
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Vector2D no;
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Vector2D co;
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r.start.x = 10;
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r.start.y = 10;
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r.direction.x = -200;
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r.direction.y = -200;
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logRay(r);
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castRaySquare(r,&no,&co);
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logVector2D(no);
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logVector2D(co);
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return 0;
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}
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