From 1b18da44dff8704b82f36d15424c7ac0583ce0ac Mon Sep 17 00:00:00 2001
From: Shahbaz Youssefi <syoussefi@chromium.org>
Date: Tue, 09 Jun 2026 13:58:24 -0400
Subject: [PATCH] Vulkan: Fix advanced blend validation + backend skip

Advanced blend is only valid when used with draw buffer 0.  When
enabled, non-0 draw buffers shouldn't be enabled.

In the Vulkan backend, blend is skipped for disabled draw buffers
because Vulkan's validation is less forgiving to mixing blend and
advanced blend for disabled attachments (See
VUID-VkPipelineColorBlendAttachmentState-advancedBlendIndependentBlend-01407)

Bug: chromium:513257423
Change-Id: I9671015fef16bcb7b170b182905d481c37c2371d
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/7914802
Reviewed-by: Amirali Abdolrashidi <abdolrashidi@google.com>
Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>
---

diff --git a/src/libANGLE/ErrorStrings.h b/src/libANGLE/ErrorStrings.h
index 6a51ec0..78dba20 100644
--- a/src/libANGLE/ErrorStrings.h
+++ b/src/libANGLE/ErrorStrings.h
@@ -17,7 +17,7 @@
 // clang-format off
 inline constexpr const char *k3DDepthStencil = "Format cannot be GL_DEPTH_COMPONENT or GL_DEPTH_STENCIL if target is GL_TEXTURE_3D.";
 inline constexpr const char *kANGLECopyTextureMissingRequiredExtension = "Copy*TextureCHROMIUM from EXTERNAL_OES to integer format requires OES_EGL_image_external_essl3.";
-inline constexpr const char *kAdvancedBlendEquationWithMRT = "Advanced blend equation can only be used when only one draw buffer is not NONE.";
+inline constexpr const char *kAdvancedBlendEquationWithMRT = "Advanced blend equations are used with a draw buffer other than draw buffer zero or with multiple draw buffers.";
 inline constexpr const char *kAtomicCounterResourceName = "Active atomic counter resources are not assigned name strings.";
 inline constexpr const char *kAttributeListNotNull = "Attribute list must be NULL or GL_NONE.";
 inline constexpr const char *kAttributeNameNull = "Attribute name is null.";
diff --git a/src/libANGLE/renderer/vulkan/ContextVk.cpp b/src/libANGLE/renderer/vulkan/ContextVk.cpp
index 59664ca..187c4db 100644
--- a/src/libANGLE/renderer/vulkan/ContextVk.cpp
+++ b/src/libANGLE/renderer/vulkan/ContextVk.cpp
@@ -4817,6 +4817,18 @@
     }
 }
 
+void ContextVk::updateBlendEnabled()
+{
+    const gl::DrawBufferMask framebufferMask = mState.getDrawFramebuffer()->getDrawBufferMask();
+    const gl::DrawBufferMask enabledBlend    = mState.getBlendStateExt().getEnabledMask();
+
+    // Filter out blend for disabled attachments.  If advanced blend is enabled, Vulkan
+    // forbids blend from being specified on the other attachments (same as GL, but GL
+    // ignores blend on disabled attachments).
+    mGraphicsPipelineDesc->updateBlendEnabled(&mGraphicsPipelineTransition,
+                                              enabledBlend & framebufferMask);
+}
+
 void ContextVk::updateBlendFuncsAndEquations()
 {
     const gl::BlendStateExt &blendStateExt = mState.getBlendStateExt();
@@ -5476,8 +5488,7 @@
                 updateDepthRange(glState.getNearPlane(), glState.getFarPlane());
                 break;
             case gl::state::DIRTY_BIT_BLEND_ENABLED:
-                mGraphicsPipelineDesc->updateBlendEnabled(
-                    &mGraphicsPipelineTransition, glState.getBlendStateExt().getEnabledMask());
+                updateBlendEnabled();
                 updateDither();
                 updateAdvancedBlendEquations(programExecutable);
                 break;
@@ -5741,6 +5752,7 @@
                                glState.getFarPlane());
                 updateColorMasks();
                 updateMissingAttachments();
+                updateBlendEnabled();
                 updateRasterizationSamples(drawFramebufferVk->getSamples());
                 updateRasterizerDiscardEnabled(
                     mState.isQueryActive(gl::QueryType::PrimitivesGenerated));
@@ -6516,6 +6528,7 @@
 
     // Attachments might have changed.
     updateMissingAttachments();
+    updateBlendEnabled();
 
     if (mState.getProgramExecutable())
     {
diff --git a/src/libANGLE/renderer/vulkan/ContextVk.h b/src/libANGLE/renderer/vulkan/ContextVk.h
index a5f8c44..24d0a5540 100644
--- a/src/libANGLE/renderer/vulkan/ContextVk.h
+++ b/src/libANGLE/renderer/vulkan/ContextVk.h
@@ -491,6 +491,7 @@
                                        gl::SamplerFormat format,
                                        gl::Texture **textureOut);
     void updateColorMasks();
+    void updateBlendEnabled();
     void updateBlendFuncsAndEquations();
 
     void handleError(VkResult errorCode,
diff --git a/src/libANGLE/renderer/vulkan/FramebufferVk.cpp b/src/libANGLE/renderer/vulkan/FramebufferVk.cpp
index 952ce67..c45ceabe 100644
--- a/src/libANGLE/renderer/vulkan/FramebufferVk.cpp
+++ b/src/libANGLE/renderer/vulkan/FramebufferVk.cpp
@@ -2758,6 +2758,7 @@
     if (shouldUpdateColorMaskAndBlend)
     {
         contextVk->updateColorMasks();
+        contextVk->updateBlendEnabled();
         contextVk->updateBlendFuncsAndEquations();
     }
 
diff --git a/src/libANGLE/validationES.cpp b/src/libANGLE/validationES.cpp
index 8f02859..d46f55f 100644
--- a/src/libANGLE/validationES.cpp
+++ b/src/libANGLE/validationES.cpp
@@ -4081,28 +4081,27 @@
         }
     }
 
-    // Advanced blend equation can only be enabled for a single render target.
+    // Advanced blend equation can only be enabled for color attachment zero and with only that
+    // attachment enabled.
     const BlendStateExt &blendStateExt = state.getBlendStateExt();
-    if (ANGLE_UNLIKELY(blendStateExt.getUsesAdvancedBlendEquationMask().any()))
+    const gl::DrawBufferMask drawBuffersWithAdvancedBlend =
+        blendStateExt.getUsesAdvancedBlendEquationMask() & blendStateExt.getEnabledMask();
+    if (ANGLE_UNLIKELY(drawBuffersWithAdvancedBlend.any()))
     {
+        // Note: Framebuffer::getDrawBufferMask() excludes non-existing draw buffers.  But if
+        // glDrawBuffers sets them to non-NONE, draw with advanced blend is still expected to fail.
+        // So we can't do a quick check with getDrawBufferMask() alone.
         const size_t drawBufferCount            = framebuffer->getDrawbufferStateCount();
-        uint32_t advancedBlendRenderTargetCount = 0;
-
-        for (size_t drawBufferIndex : blendStateExt.getUsesAdvancedBlendEquationMask())
+        const bool advancedBlendOnDrawBufferZero =
+            drawBuffersWithAdvancedBlend[0] && framebuffer->getDrawBufferState(0) != GL_NONE;
+        for (size_t drawBufferIndex = 1; drawBufferIndex < drawBufferCount; ++drawBufferIndex)
         {
-            if (drawBufferIndex < drawBufferCount &&
-                framebuffer->getDrawBufferState(drawBufferIndex) != GL_NONE &&
-                blendStateExt.getEnabledMask().test(drawBufferIndex) &&
-                blendStateExt.getUsesAdvancedBlendEquationMask().test(drawBufferIndex))
+            if (framebuffer->getDrawBufferState(drawBufferIndex) != GL_NONE &&
+                (advancedBlendOnDrawBufferZero || drawBuffersWithAdvancedBlend[drawBufferIndex]))
             {
-                ++advancedBlendRenderTargetCount;
+                return kAdvancedBlendEquationWithMRT;
             }
         }
-
-        if (advancedBlendRenderTargetCount > 1)
-        {
-            return kAdvancedBlendEquationWithMRT;
-        }
     }
 
     // Dual-source blending functions limit the number of supported draw buffers.
diff --git a/src/tests/gl_tests/AdvancedBlendTest.cpp b/src/tests/gl_tests/AdvancedBlendTest.cpp
index 15a6c49..bc79347 100644
--- a/src/tests/gl_tests/AdvancedBlendTest.cpp
+++ b/src/tests/gl_tests/AdvancedBlendTest.cpp
@@ -34,6 +34,129 @@
 class AdvancedBlendTestES32 : public AdvancedBlendTest
 {};
 
+// Test that advanced blend cannot be used when a non-zero draw buffer is enabled.
+TEST_P(AdvancedBlendTest, NonZeroDrawBufferDisallowed)
+{
+    ANGLE_SKIP_TEST_IF(!EnsureGLExtensionEnabled("GL_KHR_blend_equation_advanced"));
+
+    GLFramebuffer fbo;
+    glBindFramebuffer(GL_FRAMEBUFFER, fbo);
+
+    std::array<GLRenderbuffer, 4> rbo;
+    for (uint32_t i = 0; i < 4; ++i)
+    {
+        glBindRenderbuffer(GL_RENDERBUFFER, rbo[i]);
+        glRenderbufferStorage(GL_RENDERBUFFER, GL_RGBA8, 1, 1);
+        glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0 + i, GL_RENDERBUFFER,
+                                  rbo[i]);
+    }
+    EXPECT_GL_FRAMEBUFFER_COMPLETE(GL_FRAMEBUFFER);
+    ASSERT_GL_NO_ERROR();
+
+    GLenum enabled[4] = {GL_COLOR_ATTACHMENT0, GL_COLOR_ATTACHMENT1, GL_COLOR_ATTACHMENT2,
+                         GL_COLOR_ATTACHMENT3};
+    glDrawBuffers(4, enabled);
+
+    constexpr char kVS[] = R"(#version 300 es
+precision highp float;
+void main()
+{
+    switch (gl_VertexID)
+    {
+        case 0:  gl_Position = vec4(-1, -1, 0, 1); break;
+        case 1:  gl_Position = vec4( 3, -1, 0, 1); break;
+        default: gl_Position = vec4(-1, 3, 0, 1); break;
+    }
+})";
+
+    constexpr char kFS[] = R"(#version 300 es
+#extension GL_KHR_blend_equation_advanced : require
+layout (blend_support_multiply) out;
+precision mediump float;

diff --git a/src/tests/gl_tests/AdvancedBlendTest.cpp b/src/tests/gl_tests/AdvancedBlendTest.cpp
index 15a6c49..bc79347 100644
--- a/src/tests/gl_tests/AdvancedBlendTest.cpp
+++ b/src/tests/gl_tests/AdvancedBlendTest.cpp
@@ -34,6 +34,129 @@
 class AdvancedBlendTestES32 : public AdvancedBlendTest
 {};
 
+// Test that advanced blend cannot be used when a non-zero draw buffer is enabled.
+TEST_P(AdvancedBlendTest, NonZeroDrawBufferDisallowed)
+{
+    ANGLE_SKIP_TEST_IF(!EnsureGLExtensionEnabled("GL_KHR_blend_equation_advanced"));
+
+    GLFramebuffer fbo;
+    glBindFramebuffer(GL_FRAMEBUFFER, fbo);
+
+    std::array<GLRenderbuffer, 4> rbo;
+    for (uint32_t i = 0; i < 4; ++i)
+    {
+        glBindRenderbuffer(GL_RENDERBUFFER, rbo[i]);
+        glRenderbufferStorage(GL_RENDERBUFFER, GL_RGBA8, 1, 1);
+        glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0 + i, GL_RENDERBUFFER,
+                                  rbo[i]);
+    }
+    EXPECT_GL_FRAMEBUFFER_COMPLETE(GL_FRAMEBUFFER);
+    ASSERT_GL_NO_ERROR();
+
+    GLenum enabled[4] = {GL_COLOR_ATTACHMENT0, GL_COLOR_ATTACHMENT1, GL_COLOR_ATTACHMENT2,
+                         GL_COLOR_ATTACHMENT3};
+    glDrawBuffers(4, enabled);
+
+    constexpr char kVS[] = R"(#version 300 es
+precision highp float;
+void main()
+{
+    switch (gl_VertexID)
+    {
+        case 0:  gl_Position = vec4(-1, -1, 0, 1); break;
+        case 1:  gl_Position = vec4( 3, -1, 0, 1); break;
+        default: gl_Position = vec4(-1, 3, 0, 1); break;
+    }
+})";
+
+    constexpr char kFS[] = R"(#version 300 es
+#extension GL_KHR_blend_equation_advanced : require
+layout (blend_support_multiply) out;
+precision mediump float;
+out vec4 fragColor;
+void main()
+{
+    fragColor = vec4(1., 0., 0., 1.);
+})";
+    ANGLE_GL_PROGRAM(program, kVS, kFS);
+    glUseProgram(program);
+
+    glEnable(GL_BLEND);
+    glBlendEquation(GL_MULTIPLY_KHR);
+
+    // Invalid draw because all 4 draw buffers are enabled.
+    ASSERT_GL_NO_ERROR();
+    glDrawArrays(GL_TRIANGLES, 0, 3);
+    EXPECT_GL_ERROR(GL_INVALID_OPERATION);
+
+    enabled[1] = GL_NONE;
+    enabled[2] = GL_NONE;
+    glDrawBuffers(4, enabled);
+
+    // Still invalid because draw buffer #3 is enabled.
+    ASSERT_GL_NO_ERROR();
+    glDrawArrays(GL_TRIANGLES, 0, 3);
+    EXPECT_GL_ERROR(GL_INVALID_OPERATION);
+
+    enabled[0] = GL_NONE;
+    enabled[1] = GL_COLOR_ATTACHMENT1;
+    enabled[3] = GL_NONE;
+    glDrawBuffers(4, enabled);
+
+    // Even though a single draw buffer is enabled, it's not index 0 so it's still invalid
+    ASSERT_GL_NO_ERROR();
+    glDrawArrays(GL_TRIANGLES, 0, 3);
+    EXPECT_GL_ERROR(GL_INVALID_OPERATION);
+
+    enabled[0] = GL_COLOR_ATTACHMENT0;
+    enabled[1] = GL_NONE;
+    glDrawBuffers(4, enabled);
+
+    // When only color attachment 0 is enabled, the draw is valid.
+    glClearColor(1, 1, 1, 1);
+    glClear(GL_COLOR_BUFFER_BIT);
+    glDrawArrays(GL_TRIANGLES, 0, 3);
+    ASSERT_GL_NO_ERROR();
+    EXPECT_PIXEL_COLOR_EQ(0, 0, GLColor::red);
+
+    // It's also ok to render to multiple attachments if blend is not enabled on the attachment that
+    // has advanced blend..
+    if (EnsureGLExtensionEnabled("GL_OES_draw_buffers_indexed"))
+    {
+        // Enable two attachments
+        enabled[1] = GL_COLOR_ATTACHMENT1;
+        glDrawBuffers(4, enabled);
+
+        // Enable blend only on attachment 0
+        glDisable(GL_BLEND);
+        glEnableiOES(GL_BLEND, 0);
+        glDisableiOES(GL_BLEND, 1);
+
+        // Set advanced blend on the attachment that has blend disabled.  Set a non-advanced blend
+        // on the one that has blend enabled.
+        glBlendEquationiOES(0, GL_FUNC_ADD);
+        glBlendFunciOES(0, GL_ONE, GL_ONE);
+        glBlendEquationiOES(1, GL_MULTIPLY_KHR);
+
+        glClearColor(0, 1, 0, 1);
+        glClear(GL_COLOR_BUFFER_BIT);
+        glDrawArrays(GL_TRIANGLES, 0, 3);
+        ASSERT_GL_NO_ERROR();
+        EXPECT_PIXEL_COLOR_EQ(0, 0, GLColor::yellow);
+
+        // If advanced blend is enabled on a NONE attachment, that's also ok.
+        enabled[1] = GL_NONE;
+        glDrawBuffers(4, enabled);
+        glEnableiOES(GL_BLEND, 1);
+
+        glClearColor(0, 0, 1, 1);
+        glClear(GL_COLOR_BUFFER_BIT);
+        glDrawArrays(GL_TRIANGLES, 0, 3);
+        ASSERT_GL_NO_ERROR();
+        EXPECT_PIXEL_COLOR_EQ(0, 0, GLColor::magenta);
+    }
+}
+
 void AdvancedBlendTest::callBlendBarrier(APIExtensionVersion usedExtension)
 {
     ASSERT(usedExtension == APIExtensionVersion::Core || usedExtension == APIExtensionVersion::KHR);