Verified Commit bea32e17 authored by Jim Blandy's avatar Jim Blandy Committed by ma1
Browse files

Bug 2045796: Saturate when rounding up pixman trapezoid edges. a=diannaS DONTBUILD 

When rounding the edge coordinates of a non-antialised edge upwards,
use saturating addition, just in case the coordinates are close to the
limit of `pixman_fixed_t`'s range.

Original Revision: https://phabricator.services.mozilla.com/D314811

Differential Revision: https://phabricator.services.mozilla.com/D317287
parent 51071b8f

gfx/cairo/README

+2 −0
Original line number Diff line number Diff line
@@ -63,3 +63,5 @@ pixman-export.patch: make sure pixman symbols are not exported in libxul 
pixman-interp.patch: use lower quality interpolation by default on mobile



pixman-rename.patch: include pixman-rename.h for renaming of external symbols



pixman-edge-saturate.patch: Saturate when rounding up trapezoid edges

gfx/cairo/libpixman/src/pixman-edge-imp.h

+5 −2
Original line number Diff line number Diff line
@@ -53,10 +53,13 @@ RASTERIZE_EDGES (pixman_image_t *image, 
	 * when the sample point lies exactly on the line, we round towards

	 * north-west.

	 *

	 * Use 64 bits to get a saturating add, in case lx or rx are near

	 * the limits of pixman_fixed_t.

	 *

	 * (The AA case does a similar  adjustment in RENDER_SAMPLES_X)

	 */

	lx += X_FRAC_FIRST(1) - pixman_fixed_e;

	rx += X_FRAC_FIRST(1) - pixman_fixed_e;

	lx = (pixman_fixed_t) MIN ((int64_t) lx + (X_FRAC_FIRST(1) - pixman_fixed_e), INT32_MAX);

	rx = (pixman_fixed_t) MIN ((int64_t) rx + (X_FRAC_FIRST(1) - pixman_fixed_e), INT32_MAX);

#endif

	/* clip X */

	if (lx < 0)

gfx/cairo/pixman-edge-saturate.patch

0 → 100644
+23 −0
Original line number Diff line number Diff line 
From: Jim Blandy <jimb@mozilla.com>

Subject: Saturate when rounding up trapezoid edges



diff --git a/gfx/cairo/libpixman/src/pixman-edge-imp.h b/gfx/cairo/libpixman/src/pixman-edge-imp.h

index a4698eddb281..39e8d71d2568 100644

--- a/gfx/cairo/libpixman/src/pixman-edge-imp.h

+++ b/gfx/cairo/libpixman/src/pixman-edge-imp.h

@@ -53,10 +53,13 @@ RASTERIZE_EDGES (pixman_image_t  *image,

 	 * when the sample point lies exactly on the line, we round towards

 	 * north-west.

 	 *

+	 * Use 64 bits to get a saturating add, in case lx or rx are near

+	 * the limits of pixman_fixed_t.

+	 *

 	 * (The AA case does a similar  adjustment in RENDER_SAMPLES_X)

 	 */

-	lx += X_FRAC_FIRST(1) - pixman_fixed_e;

-	rx += X_FRAC_FIRST(1) - pixman_fixed_e;

+	lx = (pixman_fixed_t) MIN ((int64_t) lx + (X_FRAC_FIRST(1) - pixman_fixed_e), INT32_MAX);

+	rx = (pixman_fixed_t) MIN ((int64_t) rx + (X_FRAC_FIRST(1) - pixman_fixed_e), INT32_MAX);

 #endif

 	/* clip X */

 	if (lx < 0)