From 9ce3268f4c4b0383b27ab28919e37ead03528c72 Mon Sep 17 00:00:00 2001
From: Shahbaz Youssefi <[email protected]>
Date: Wed, 20 May 2026 16:36:42 -0400
Subject: [PATCH] Ensure maxColorAttachments == mDrawBufferStates in Caps

In GLES, glDrawBuffers requires that draw buffers are mapped to either
GL_NONE or the color attachment with the same index.  ANGLE does not
distinguish between draw buffer and color attachment indices in many
places, so this change makes sure their limits are also identical.

This is a theoretical fix for a driver where maxColorAttachments >
maxDrawBuffers, which doesn't exist AFAICT.

Bug: chromium:513918431
Change-Id: I70a3829360df27d88d69224d75219b9d604a792f
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/7864741
Reviewed-by: Geoff Lang <[email protected]>
Commit-Queue: Shahbaz Youssefi <[email protected]>
---

diff --git a/src/libANGLE/Context.cpp b/src/libANGLE/Context.cpp
index c3568e5..2b24785 100644
--- a/src/libANGLE/Context.cpp
+++ b/src/libANGLE/Context.cpp
@@ -4307,12 +4307,18 @@
         }                                      \
     } while (0)
 
-    // Apply/Verify implementation limits
-    ANGLE_LIMIT_CAP(caps->maxDrawBuffers, IMPLEMENTATION_MAX_DRAW_BUFFERS);
+    // Apply/Verify implementation limits.
+    //
+    // GLES requires that draw buffers are mapped to color attachments with an identical index (in
+    // glDrawBuffers), and so draw buffers and color attachments are frequently interchanged in the
+    // codebase.  The same limit is thus used for both.
+    const GLint maxDrawBuffersAndColorAttachments = std::min<GLint>(
+        std::min(caps->maxDrawBuffers, caps->maxColorAttachments), IMPLEMENTATION_MAX_DRAW_BUFFERS);
+    ANGLE_LIMIT_CAP(caps->maxDrawBuffers, maxDrawBuffersAndColorAttachments);
     ANGLE_LIMIT_CAP(caps->maxFramebufferWidth, IMPLEMENTATION_MAX_FRAMEBUFFER_SIZE);
     ANGLE_LIMIT_CAP(caps->maxFramebufferHeight, IMPLEMENTATION_MAX_FRAMEBUFFER_SIZE);
     ANGLE_LIMIT_CAP(caps->maxRenderbufferSize, IMPLEMENTATION_MAX_RENDERBUFFER_SIZE);
-    ANGLE_LIMIT_CAP(caps->maxColorAttachments, IMPLEMENTATION_MAX_DRAW_BUFFERS);
+    ANGLE_LIMIT_CAP(caps->maxColorAttachments, maxDrawBuffersAndColorAttachments);
     ANGLE_LIMIT_CAP(caps->maxVertexAttributes, MAX_VERTEX_ATTRIBS);
     if (mDisplay->getFrontendFeatures().forceMinimumMaxVertexAttributes.enabled &&
         getClientVersion() <= Version(2, 0))