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Cleanup: simplify bitmap line drawing 

- Expand overly dense & confusing delta assignments.
- Replace bit shift with multiply.

Also link to 'clipped' version of this function
which may be useful to add later.
This commit is contained in:
Campbell Barton 2016-12-04 15:05:50 +11:00
parent 923eae25d1
commit d9d7b5b4d0
1 changed files with 24 additions and 19 deletions
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43
source/blender/blenlib/intern/bitmap_draw_2d.c
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@ -46,6 +46,8 @@
/**
* Plot a line from \a p1 to \a p2 (inclusive).
*
* \note For clipped line drawing, see: http://stackoverflow.com/a/40902741/432509
*/
void BLI_bitmap_draw_2d_line_v2v2i(
const int p1[2], const int p2[2],
@ -57,33 +59,36 @@ void BLI_bitmap_draw_2d_line_v2v2i(
int x2 = p2[0];
int y2 = p2[1];
int ix;
int iy;
/* if x1 == x2 or y1 == y2, then it does not matter what we set here */
int delta_x = (x2 > x1 ? ((void)(ix = 1), x2 - x1) : ((void)(ix = -1), x1 - x2)) << 1;
int delta_y = (y2 > y1 ? ((void)(iy = 1), y2 - y1) : ((void)(iy = -1), y1 - y2)) << 1;
if (callback(x1, y1, userData) == 0) {
return;
}
/* if x1 == x2 or y1 == y2, then it does not matter what we set here */
const int sign_x = (x2 > x1) ? 1 : -1;
const int sign_y = (y2 > y1) ? 1 : -1;
const int delta_x = (sign_x == 1) ? (x2 - x1) : (x1 - x2);
const int delta_y = (sign_y == 1) ? (y2 - y1) : (y1 - y2);
const int delta_x_step = delta_x * 2;
const int delta_y_step = delta_y * 2;
if (delta_x >= delta_y) {
/* error may go below zero */
int error = delta_y - (delta_x >> 1);
int error = delta_y_step - delta_x;
while (x1 != x2) {
if (error >= 0) {
if (error || (ix > 0)) {
y1 += iy;
error -= delta_x;
if (error || (sign_x == 1)) {
y1 += sign_y;
error -= delta_x_step;
}
/* else do nothing */
}
/* else do nothing */
x1 += ix;
error += delta_y;
x1 += sign_x;
error += delta_y_step;
if (callback(x1, y1, userData) == 0) {
return;
@ -92,20 +97,20 @@ void BLI_bitmap_draw_2d_line_v2v2i(
}
else {
/* error may go below zero */
int error = delta_x - (delta_y >> 1);
int error = delta_x_step - delta_y;
while (y1 != y2) {
if (error >= 0) {
if (error || (iy > 0)) {
x1 += ix;
error -= delta_y;
if (error || (sign_y == 1)) {
x1 += sign_x;
error -= delta_y_step;
}
/* else do nothing */
}
/* else do nothing */
y1 += iy;
error += delta_x;
y1 += sign_y;
error += delta_x_step;
if (callback(x1, y1, userData) == 0) {
return;