weston: add bbappend to apply gl-shader patch (#1881)

Weston currently relies on shader compiler optimizations that are not
guaranteed across all GPU implementations. When unused YUV shader
uniforms are not optimized out, this leads to assertion failures and
crashes on some platforms.

Backport the upstream fix using a Weston .bbappend to ensure consistent
behavior across GPU drivers in Yocto builds, without altering the
upstream recipe.

Author: ricardosalveti

recipes-graphics/wayland/weston/0001-gl-shaders-Remove-asserts-relying-on-shader-compiler.patch

@@ -0,0 +1,47 @@
+From 5c49563ef49a502a6b8fae44f8778e109d32c2d9 Mon Sep 17 00:00:00 2001
+From: Robert Mader <robert.mader@collabora.com>
+Date: Mon, 2 Mar 2026 13:11:05 +0100
+Subject: [PATCH] gl-shaders: Remove asserts relying on shader compiler
+ behavior
+
+yuv_coefficients and yuv_offsets should get optimized away by shader
+compilers as the related code paths can never be reached. This seems to
+work well on Mesa but not necessarily with other drivers.
+
+While on it, assert that the uniforms *are* present, unless the
+yuv-to-rgb conversion is handled by the driver.
+
+Upstream-Status: Backport [https://gitlab.freedesktop.org/wayland/weston/-/commit/5c49563ef49a502a6b8fae44f8778e109d32c2d9]
+Signed-off-by: Robert Mader <robert.mader@collabora.com>
+---
+ libweston/renderer-gl/gl-shaders.c | 14 ++++++++++++--
+ 1 file changed, 12 insertions(+), 2 deletions(-)
+
+diff --git a/libweston/renderer-gl/gl-shaders.c b/libweston/renderer-gl/gl-shaders.c
+index 98041882..18eeedf6 100644
+--- a/libweston/renderer-gl/gl-shaders.c
++++ b/libweston/renderer-gl/gl-shaders.c
+@@ -762,8 +762,18 @@ gl_shader_load_config_representation(struct weston_compositor *compositor,
+ 
+ 	if (sconf->yuv_coefficients == WESTON_COLOR_MATRIX_COEF_UNSET ||
+ 	    sconf->yuv_coefficients == WESTON_COLOR_MATRIX_COEF_IDENTITY) {
+-		assert(shader->yuv_coefficients_uniform == -1);
+-		assert(shader->yuv_offsets_uniform == -1);
++		/*
++		 * In this case the yuv_coefficients and yuv_offsets uniforms
++		 * should never be used and thus get optimized away by the
++		 * shader compiler. Unfortunately on some drivers this is not
++		 * the case, so we can't assert on it.
++		 */
++		return;
++	}
++
++	if (shader->yuv_coefficients_uniform == -1 ||
++	    shader->yuv_offsets_uniform == -1) {
++		assert(shader->key.variant == SHADER_VARIANT_EXTERNAL);
+ 		return;
+ 	}
+ 
+-- 
+2.34.1
+

recipes-graphics/wayland/weston_15.0.0.bbappend

@@ -0,0 +1,5 @@
+FILESEXTRAPATHS:prepend := "${THISDIR}/${PN}:"
+
+SRC_URI:append:qcom = " \
+    file://0001-gl-shaders-Remove-asserts-relying-on-shader-compiler.patch \
+"