# --- T2-COPYRIGHT-BEGIN ---
# t2/package/*/firefox/hotfix-swgl-linear-gradient-zero-delta.patch
# Copyright (C) 2026 The T2 SDE Project
# SPDX-License-Identifier: GPL-2.0 or patched project license
# --- T2-COPYRIGHT-END ---

# SWGL walks a vertical linear gradient one pixel at a time.
#
# commitLinearGradientFromStops() computes how many pixels the current gradient
# stop pair covers by intersecting the span with the next stop offset:
#
#     offsetRange = delta > 0 ? nextOffset - offset.x : prevOffset - offset.x;
#     subSpan = min(subSpan, offsetRange / delta);
#
# delta is the change in gradient offset per pixel, dot(dFdx(pos), scaleDir).
# For a vertical gradient scaleDir has no x component, so along a horizontal
# span delta is exactly 0 and the offset - and therefore the color - is
# constant for the entire span.
#
# delta == 0 is not > 0, so the else branch is taken and offsetRange becomes
# prevOffset - offset.x, which is negative. Dividing by a zero delta gives
# -inf, and the following
#
#     subSpan = max(ceil(subSpan), 1.0f);
#
# pins subSpan to 1. The span is then emitted a single pixel at a time, paying
# a stop-pair search, a reciprocal and a full color setup per pixel, and never
# reaching the 4-pixel chunk loop - for a span that is one flat color.

--- firefox-154.0.1/gfx/wr/swgl/src/swgl_ext.h.vanilla
+++ firefox-154.0.1/gfx/wr/swgl/src/swgl_ext.h
@@ -1981,9 +1981,11 @@
       stopIndex =
           findGradientStopPair(offset.x, stopOffsets, stopCount,
                                prevOffset, nextOffset);
-      float offsetRange =
-          delta > 0.0f ? nextOffset - offset.x : prevOffset - offset.x;
-      subSpan = min(subSpan, offsetRange / delta);
+      if (delta != 0.0f) {
+        float offsetRange =
+            delta > 0.0f ? nextOffset - offset.x : prevOffset - offset.x;
+        subSpan = min(subSpan, offsetRange / delta);
+      }
     }
 
     // Ensure that we advance by at least a pixel.