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Fix PC bug

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This commit is contained in:
Miloslav Číž 2019-06-12 00:03:23 +02:00
parent d63b23c6d9
commit 0deafc2da6
1 changed files with 57 additions and 21 deletions
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44
small3dlib.h
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@ -1990,23 +1990,58 @@ void S3L_drawTriangle(
#elif S3L_PERSPECTIVE_CORRECTION == 2
if (rowCount >= S3L_PC_APPROX_LENGTH)
{
// init the linear interpolation to the next PC correct value
rowCount = 0;
S3L_Unit nextI = i + S3L_PC_APPROX_LENGTH;
S3L_Unit nextDepth =
if (nextI >= rowLength)
{
/* A special case where we'd be interpolating outside the triangle.
It seems like a valid approach at first, but it creates a bug
in a case when the rasaterized triangle is near screen 0 and can
actually never reach the extrapolated screen position. So we
have to clamp to the actual end of the triangle here. */
S3L_Unit maxI = S3L_nonZero(rowLength - i);
S3L_Unit nextDepthScaled =
(
(S3L_FRACTIONS_PER_UNIT * S3L_FRACTIONS_PER_UNIT) /
S3L_nonZero(rRecipZ)
) << S3L_FAST_LERP_QUALITY;
depthPC.stepScaled =
(nextDepthScaled - depthPC.valueScaled) / maxI;
S3L_Unit nextValue =
(
rOverZ
* nextDepthScaled
) / S3L_FRACTIONS_PER_UNIT;
b0PC.stepScaled =
(nextValue - b0PC.valueScaled) / maxI;
b1PC.stepScaled =
-1 * b1PC.valueScaled / maxI;
}
else
{
S3L_Unit nextDepthScaled =
(
(S3L_FRACTIONS_PER_UNIT * S3L_FRACTIONS_PER_UNIT) /
S3L_nonZero(S3L_interpolate(lRecipZ,rRecipZ,nextI,rowLength))
) << S3L_FAST_LERP_QUALITY;
depthPC.stepScaled =
(nextDepth - depthPC.valueScaled) / S3L_PC_APPROX_LENGTH;
(nextDepthScaled - depthPC.valueScaled) / S3L_PC_APPROX_LENGTH;
S3L_Unit nextValue =
(
S3L_interpolateFrom0(rOverZ,nextI,rowLength)
* nextDepth
* nextDepthScaled
) / S3L_FRACTIONS_PER_UNIT;
b0PC.stepScaled =
@ -2015,12 +2050,13 @@ void S3L_drawTriangle(
nextValue =
(
(lOverZ - S3L_interpolateFrom0(lOverZ,nextI,rowLength))
* nextDepth
* nextDepthScaled
) / S3L_FRACTIONS_PER_UNIT;
b1PC.stepScaled =
(nextValue - b1PC.valueScaled) / S3L_PC_APPROX_LENGTH;
}
}
p.depth = S3L_getFastLerpValue(depthPC);
#else