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ImageDrawLine shortened significantly using maths

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Substituted X and Y, then wrote one abstract loop instead of 4 specific loops.
Lots of comments to explain what I'm doing for future maintainers.
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Alexander Buhl 2021-07-20 23:15:50 +02:00 committed by GitHub
parent 6a01c3f31a
commit 83d0974525
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1 changed files with 76 additions and 113 deletions
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151
src/textures.c
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@ -2426,129 +2426,92 @@ void ImageDrawLine (Image *dst, int startPosX, int startPosY, int endPosX, int e
int changeInY = (endPosY - startPosY);
int abs_changeInY = changeInY < 0 ? -changeInY : changeInY;
if (abs_changeInY < abs_changeInX)
int startU, startV, endU, V_step; // Substitutions, either U = X, V = Y or vice versa. See loop at end of function
//int endV; // We never need this, i didn't just forget about it! :D
// For understanding I left it in below, too.
int A, B, P; // See linked paper above. Explained down in the main loop.
int is_x_y_reversed = (abs_changeInY < abs_changeInX);
if (is_x_y_reversed)
{
A = 2* abs_changeInY;
B = A - 2* abs_changeInX;
P = A - abs_changeInX;
if (changeInX > 0)
{
// we need to go up or down depending (-1 or 1);
int y_directional_unit = changeInY < 0 ? -1 : 1;
int A = 2* abs_changeInY;
int B = A - 2* abs_changeInX;
int P = A - abs_changeInX;
ImageDrawPixel(dst, startPosX, startPosY, color);
for (int x = startPosX+1, y = startPosY; x <= endPosX; x += 1)
{
if (P >= 0)
{
y += y_directional_unit;
P += B;
startU = startPosX;
startV = startPosY;
endU = endPosX;
//endV = endPosY;
}
else
{
P += A;
}
ImageDrawPixel(dst, x, y, color);
}
}
else
{
// doing the equivalent of "calling" the branch above with inverted parameters:
startU = endPosX;
startV = endPosY;
endU = startPosX;
//endV = startPosY;
// since start and end are reversed:
changeInX = -changeInX;
changeInY = -changeInY;
int help;
help = startPosX;
startPosX = endPosX;
endPosX = help;
help = startPosY;
startPosY = endPosY;
endPosY = help;
}
int y_directional_unit = changeInY < 0 ? -1 : 1;
V_step = changeInY < 0 ? -1 : 1;
int A = 2* abs_changeInY;
int B = A - 2* abs_changeInX;
int P = A - abs_changeInX;
ImageDrawPixel(dst, startU, startV, color); // At this point they are correctly ordered...
}
else // all X and Y are reversed in here:
{
A = 2* abs_changeInX;
B = A - 2* abs_changeInY;
P = A - abs_changeInY;
ImageDrawPixel(dst, startPosX, startPosY, color);
for (int x = startPosX+1, y = startPosY; x <= endPosX; x += 1)
{
if (P >= 0)
{
y += y_directional_unit;
P += B;
}
else
{
P += A;
}
ImageDrawPixel(dst, x, y, color);
}
}
}
else
{
if (changeInY > 0)
{
int x_directional_unit = changeInX < 0 ? -1 : 1;
int A = 2* abs_changeInX;
int B = A - 2* abs_changeInY;
int P = A - abs_changeInY;
ImageDrawPixel(dst, startPosX, startPosY, color);
for (int y = startPosY+1, x = startPosX; y <= endPosY; y += 1)
{
if (P >= 0)
{
x += x_directional_unit;
P += B;
startU = startPosY;
startV = startPosX;
endU = endPosY;
//endV = endPosX;
}
else
{
P += A;
}
ImageDrawPixel(dst, x, y, color);
}
}
else
{
// doing the equivalent of "calling" the branch above with inverted parameters:
startU = endPosY;
startV = endPosX;
endU = startPosY;
//endV = startPosX;
// since start and end are reversed:
changeInX = -changeInX;
changeInY = -changeInY;
int help;
help = startPosX;
startPosX = endPosX;
endPosX = help;
help = startPosY;
startPosY = endPosY;
endPosY = help;
}
int x_directional_unit = changeInX < 0 ? -1 : 1;
V_step = changeInX < 0 ? -1 : 1;
int A = 2* abs_changeInX;
int B = A - 2* abs_changeInY;
int P = A - abs_changeInY;
ImageDrawPixel(dst, startV, startU, color); // ... but need to be reversed here. Repeated in the main loop below.
}
ImageDrawPixel(dst, startPosX, startPosY, color);
for (int y = startPosY+1, x = startPosX; y <= endPosY; y += 1)
// We already drew the start point. If we started at startU+0, the line would be crooked and too short.
for (int U = startU+1, V = startV; U <= endU; U += 1)
{
if (P >= 0)
{
x += x_directional_unit;
P += B;
V += V_step; // Adjusts whenever we stray too far from the direct line. Details in the linked paper above.
P += B; // Remembers that we corrected our path.
}
else
{
P += A;
P += A; // Remembers how far we are from the direct line.
}
ImageDrawPixel(dst, x, y, color);
if (is_x_y_reversed) // Substitutions may be in wrong order for drawing:
{
ImageDrawPixel(dst, U, V, color);
}
else
{
ImageDrawPixel(dst, V, U, color);
}
}
}