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(svn r25119) -Codechange [FS#5512]: Improve the clipping/visiblity check before sending lines to blitter for drawing. (fonsinchen)

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frosch 2013-03-24 11:54:37 +00:00
parent 166513bbd4
commit 79185e7a2b
1 changed files with 67 additions and 8 deletions
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75
src/gfx.cpp
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@ -191,6 +191,71 @@ void GfxFillRect(int left, int top, int right, int bottom, int colour, FillRectM
}
}
/**
* Check line clipping by using a linear equation and draw the visible part of
* the line given by x/y and x2/y2.
* @param video Destination pointer to draw into.
* @param x X coordinate of first point.
* @param y Y coordinate of first point.
* @param x2 X coordinate of second point.
* @param y2 Y coordinate of second point.
* @param screen_width With of the screen to check clipping against.
* @param screen_height Height of the screen to check clipping against.
* @param colour Colour of the line.
* @param width Width of the line.
*/
static inline void GfxDoDrawLine(void *video, int x, int y, int x2, int y2, int screen_width, int screen_height, uint8 colour, int width)
{
Blitter *blitter = BlitterFactoryBase::GetCurrentBlitter();
assert(width > 0);
if (y2 == y) {
/* Special case: horizontal line. */
blitter->DrawLine(video,
Clamp(x, 0, screen_width), y,
Clamp(x2, 0, screen_width), y2,
screen_width, screen_height, colour, width);
return;
}
if (x2 == x) {
/* Special case: vertical line. */
blitter->DrawLine(video,
x, Clamp(y, 0, screen_height),
x2, Clamp(y2, 0, screen_height),
screen_width, screen_height, colour, width);
return;
}
int grade_y = y2 - y;
int grade_x = x2 - x;
/* prevent integer overflows. */
int margin = 1;
while (INT_MAX / abs(grade_y) < max(abs(x), abs(screen_width - x))) {
grade_y /= 2;
grade_x /= 2;
margin *= 2; // account for rounding errors
}
/* If the line is outside the screen on the same side at X positions 0
* and screen_width, we don't need to draw anything. */
int offset_0 = y - x * grade_y / grade_x;
int offset_width = y + (screen_width - x) * grade_y / grade_x;
if ((offset_0 > screen_height + width / 2 + margin && offset_width > screen_height + width / 2 + margin) ||
(offset_0 < -width / 2 - margin && offset_width < -width / 2 - margin)) {
return;
}
/* It is possible to use the line equation to further reduce the amount of
* work the blitter has to do by shortening the effective line segment.
* However, in order to get that right and prevent the flickering effects
* of rounding errors so much additional code has to be run here that in
* the general case the effect is not noticable. */
blitter->DrawLine(video, x, y, x2, y2, screen_width, screen_height, colour, width);
}
/**
* Align parameters of a line to the given DPI and check simple clipping.
* @param dpi Screen parameters to align with.
@ -219,23 +284,17 @@ static inline bool GfxPreprocessLine(DrawPixelInfo *dpi, int &x, int &y, int &x2
void GfxDrawLine(int x, int y, int x2, int y2, int colour, int width)
{
Blitter *blitter = BlitterFactoryBase::GetCurrentBlitter();
DrawPixelInfo *dpi = _cur_dpi;
assert(width > 0);
if (GfxPreprocessLine(dpi, x, y, x2, y2, width)) {
blitter->DrawLine(dpi->dst_ptr, x, y, x2, y2, dpi->width, dpi->height, colour, width);
GfxDoDrawLine(dpi->dst_ptr, x, y, x2, y2, dpi->width, dpi->height, colour, width);
}
}
void GfxDrawLineUnscaled(int x, int y, int x2, int y2, int colour)
{
Blitter *blitter = BlitterFactoryBase::GetCurrentBlitter();
DrawPixelInfo *dpi = _cur_dpi;
if (GfxPreprocessLine(dpi, x, y, x2, y2, 1)) {
blitter->DrawLine(dpi->dst_ptr,
GfxDoDrawLine(dpi->dst_ptr,
UnScaleByZoom(x, dpi->zoom), UnScaleByZoom(y, dpi->zoom),
UnScaleByZoom(x2, dpi->zoom), UnScaleByZoom(y2, dpi->zoom),
UnScaleByZoom(dpi->width, dpi->zoom), UnScaleByZoom(dpi->height, dpi->zoom), colour, 1);