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vwebp: fix incorrect clipping w/NO_BLEND

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when the previous frame does not specify dispose to background only the
current frame's rectangle should be cleared

related to bug #245

(cherry picked from commit 469ba2cdfd)

Change-Id: I2fc4f5be99057e0bf87d8fedec57b06859b070bd
This commit is contained in:
Pascal Massimino 2015-10-23 00:01:24 -07:00 committed by James Zern
parent fcfde90b9c
commit 46e18c0a25
1 changed files with 6 additions and 1 deletions
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7
examples/vwebp.c
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@ -308,19 +308,24 @@ static void HandleDisplay(void) {
// they will be incorrect if the window is resized.
// glScissor() takes window coordinates (0,0 at bottom left).
int window_x, window_y;
int frame_w, frame_h;
if (prev->dispose_method == WEBP_MUX_DISPOSE_BACKGROUND) {
// Clear the previous frame rectangle.
window_x = prev->x_offset;
window_y = kParams.canvas_height - prev->y_offset - prev->height;
frame_w = prev->width;
frame_h = prev->height;
} else { // curr->blend_method == WEBP_MUX_NO_BLEND.
// We simulate no-blending behavior by first clearing the current frame
// rectangle (to a checker-board) and then alpha-blending against it.
window_x = curr->x_offset;
window_y = kParams.canvas_height - curr->y_offset - curr->height;
frame_w = curr->width;
frame_h = curr->height;
}
glEnable(GL_SCISSOR_TEST);
// Only update the requested area, not the whole canvas.
glScissor(window_x, window_y, prev->width, prev->height);
glScissor(window_x, window_y, frame_w, frame_h);
glClear(GL_COLOR_BUFFER_BIT); // use clear color
DrawCheckerBoard();