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(svn r27322) -Fix: Clipping of inclined lines did not account for the 'horizontal width' being bigger than the 'real width'. (adf88)

release/1.6
frosch 2015-06-28 15:50:13 +00:00
parent bddcd33ed7
commit a65a194416
1 changed files with 13 additions and 7 deletions
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20
src/gfx.cpp
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@ -195,20 +195,26 @@ static inline void GfxDoDrawLine(void *video, int x, int y, int x2, int y2, int
int grade_y = y2 - y; int grade_y = y2 - y;
int grade_x = x2 - x; int grade_x = x2 - x;
/* Clipping rectangle. Slightly extended so we can ignore the width of the line. */
uint extra = CeilDiv(3 * width, 4); // not less then "width * sqrt(2) / 2"
Rect clip = { -extra, -extra, screen_width - 1 + extra, screen_height - 1 + extra };
/* prevent integer overflows. */ /* prevent integer overflows. */
int margin = 1; int margin = 1;
while (INT_MAX / abs(grade_y) < max(abs(x), abs(screen_width - x))) { while (INT_MAX / abs(grade_y) < max(abs(clip.left - x), abs(clip.right - x))) {
grade_y /= 2; grade_y /= 2;
grade_x /= 2; grade_x /= 2;
margin *= 2; // account for rounding errors margin *= 2; // account for rounding errors
} }
/* If the line is outside the screen on the same side at X positions 0 /* Imagine that the line is infinitely long and it intersects with
* and screen_width, we don't need to draw anything. */ * infinitely long left and right edges of the clipping rectangle.
int offset_0 = y - x * grade_y / grade_x; * If booth intersection points are outside the clipping rectangle
int offset_width = y + (screen_width - x) * grade_y / grade_x; * and booth on the same side of it, we don't need to draw anything. */
if ((offset_0 > screen_height + width / 2 + margin && offset_width > screen_height + width / 2 + margin) || int left_isec_y = y + (clip.left - x) * grade_y / grade_x;
(offset_0 < -width / 2 - margin && offset_width < -width / 2 - margin)) { int right_isec_y = y + (clip.right - x) * grade_y / grade_x;
if ((left_isec_y > clip.bottom + margin && right_isec_y > clip.bottom + margin) ||
(left_isec_y < clip.top - margin && right_isec_y < clip.top - margin)) {
return; return;
} }