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[clip-stack] Handle flipped rectangles in try_pushing_rect_as_window_rect()

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We were ignoring the possibility that the current modelview matrix may flip
the incoming rectangle in which case we didn't calculate a valid scissor
rectangle for clipping.

This fixes: http://bugzilla.o-hand.com/show_bug.cgi?id=1809
(Clipping doesn't work within an FBO)
This commit is contained in:
Robert Bragg 2009-10-17 00:31:26 +01:00
parent bb3a008318
commit 49db9f4f77
1 changed files with 18 additions and 0 deletions
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18
cogl/cogl-clip-stack.c
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@ -203,6 +203,15 @@ try_pushing_rect_as_window_rect (float x_offset,
cogl_get_modelview_matrix (&matrix);
/* If the modelview meets these constraints then a transformed rectangle
* should still be a rectangle when it reaches screen coordinates.
*
* FIXME: we are are making certain assumptions about the projection
* matrix a.t.m and should really be looking at the combined modelview
* and projection matrix.
* FIXME: we don't consider rotations that are a multiple of 90 degrees
* which could be quite common.
*/
if (matrix.xy != 0 || matrix.xz != 0 ||
matrix.yx != 0 || matrix.yz != 0 ||
matrix.zx != 0 || matrix.zy != 0)
@ -214,6 +223,15 @@ try_pushing_rect_as_window_rect (float x_offset,
transform_point (&matrix, &matrix_p, v, &_x0, &_y0);
transform_point (&matrix, &matrix_p, v, &_x1, &_y1);
/* Consider that the modelview matrix may flip the rectangle
* along the x or y axis... */
#define SWAP(A,B) do { float tmp = B; B = A; A = tmp; } while (0)
if (_x0 > _x1)
SWAP (_x0, _x1);
if (_y0 > _y1)
SWAP (_y0, _y1);
#undef SWAP
cogl_clip_push_window_rect (_x0, _y0, _x1 - _x0, _y1 - _y0);
return TRUE;
}