Prefer to use the OES_depth24 extension for WebGL's depth-only back buffers.

third_party/WebKit/Source/platform/graphics/gpu/DrawingBuffer.cpp

 /*
  * Copyright (c) 2010, Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 86 matching lines @@
         return nullptr;
     }
 
     OwnPtr<Extensions3DUtil> extensionsUtil = Extensions3DUtil::create(context.get());
     if (!extensionsUtil->isValid()) {
         // This might be the first time we notice that the WebGraphicsContext3D is lost.
         return nullptr;
     }
     ASSERT(extensionsUtil->supportsExtension("GL_OES_packed_depth_stencil"));
     extensionsUtil->ensureExtensionEnabled("GL_OES_packed_depth_stencil");
-    bool multisampleSupported = (extensionsUtil->supportsExtension("GL_CHROMIUM_framebuffer_multisample")
+
+    SupportedExtensions exts;
+    exts.multisample = (extensionsUtil->supportsExtension("GL_CHROMIUM_framebuffer_multisample")
         || extensionsUtil->supportsExtension("GL_EXT_multisampled_render_to_texture"))
         && extensionsUtil->supportsExtension("GL_OES_rgb8_rgba8");
-    if (multisampleSupported) {
+    if (exts.multisample) {
         extensionsUtil->ensureExtensionEnabled("GL_OES_rgb8_rgba8");
         if (extensionsUtil->supportsExtension("GL_CHROMIUM_framebuffer_multisample"))
             extensionsUtil->ensureExtensionEnabled("GL_CHROMIUM_framebuffer_multisample");
         else
             extensionsUtil->ensureExtensionEnabled("GL_EXT_multisampled_render_to_texture");
     }
-    bool discardFramebufferSupported = extensionsUtil->supportsExtension("GL_EXT_discard_framebuffer");
-    if (discardFramebufferSupported)
+    exts.packedDepthStencil = true;
+    exts.depth24 = extensionsUtil->supportsExtension("GL_OES_depth24");
+    if (exts.depth24)
+        extensionsUtil->ensureExtensionEnabled("GL_OES_depth24");
+    exts.discardFramebuffer = extensionsUtil->supportsExtension("GL_EXT_discard_framebuffer");
+    if (exts.discardFramebuffer)
         extensionsUtil->ensureExtensionEnabled("GL_EXT_discard_framebuffer");
 
-    RefPtr<DrawingBuffer> drawingBuffer = adoptRef(new DrawingBuffer(std::move(context), extensionsUtil.release(), multisampleSupported, true, discardFramebufferSupported, preserve, requestedAttributes));
+    RefPtr<DrawingBuffer> drawingBuffer = adoptRef(new DrawingBuffer(std::move(context), extensionsUtil.release(), exts, preserve, requestedAttributes));
     if (!drawingBuffer->initialize(size)) {
         drawingBuffer->beginDestruction();
         return PassRefPtr<DrawingBuffer>();
     }
     return drawingBuffer.release();
 }
 
 void DrawingBuffer::forceNextDrawingBufferCreationToFail()
 {
     shouldFailDrawingBufferCreationForTesting = true;
 }
 
+DrawingBuffer::SupportedExtensions::SupportedExtensions() :
+    multisample(false), packedDepthStencil(false), depth24(false), discardFramebuffer(false) {}
+
 DrawingBuffer::DrawingBuffer(PassOwnPtr<WebGraphicsContext3D> context,
     PassOwnPtr<Extensions3DUtil> extensionsUtil,
-    bool multisampleExtensionSupported,
-    bool packedDepthStencilExtensionSupported,
-    bool discardFramebufferSupported,
+    const SupportedExtensions& supportedExtensions,
     PreserveDrawingBuffer preserve,
     WebGraphicsContext3D::Attributes requestedAttributes)
     : m_preserveDrawingBuffer(preserve)
     , m_scissorEnabled(false)
     , m_texture2DBinding(0)
     , m_drawFramebufferBinding(0)
     , m_readFramebufferBinding(0)
     , m_activeTextureUnit(GL_TEXTURE0)
     , m_context(std::move(context))
     , m_extensionsUtil(std::move(extensionsUtil))
     , m_size(-1, -1)
     , m_requestedAttributes(requestedAttributes)
-    , m_multisampleExtensionSupported(multisampleExtensionSupported)
-    , m_packedDepthStencilExtensionSupported(packedDepthStencilExtensionSupported)
-    , m_discardFramebufferSupported(discardFramebufferSupported)
+    , m_multisampleExtensionSupported(supportedExtensions.multisample)
+    , m_packedDepthStencilExtensionSupported(supportedExtensions.packedDepthStencil)
+    , m_depth24ExtensionSupported(supportedExtensions.depth24)
+    , m_discardFramebufferSupported(supportedExtensions.discardFramebuffer)
     , m_fbo(0)
     , m_depthStencilBuffer(0)
     , m_depthBuffer(0)
     , m_stencilBuffer(0)
     , m_multisampleFBO(0)
     , m_multisampleColorBuffer(0)
     , m_contentsChanged(true)
     , m_contentsChangeCommitted(false)
     , m_bufferClearNeeded(false)
     , m_antiAliasingMode(None)
@@ skipping 526 matching lines @@
     }
 
     return true;
 }
 
 void DrawingBuffer::resizeDepthStencil(const IntSize& size)
 {
     if (!m_requestedAttributes.depth && !m_requestedAttributes.stencil)
         return;
 
-    if (m_packedDepthStencilExtensionSupported) {
+    if (m_requestedAttributes.depth && !m_requestedAttributes.stencil && m_depth24ExtensionSupported) {
+        if (!m_depthBuffer)
+            m_depthBuffer = m_context->createRenderbuffer();
+        m_context->bindRenderbuffer(GL_RENDERBUFFER, m_depthBuffer);
+        if (m_antiAliasingMode == MSAAImplicitResolve)
+            m_context->renderbufferStorageMultisampleEXT(GL_RENDERBUFFER, m_sampleCount, GL_DEPTH_COMPONENT24, size.width(), size.height());
+        else if (m_antiAliasingMode == MSAAExplicitResolve)
+            m_context->renderbufferStorageMultisampleCHROMIUM(GL_RENDERBUFFER, m_sampleCount, GL_DEPTH_COMPONENT24, size.width(), size.height());
+        else
+            m_context->renderbufferStorage(GL_RENDERBUFFER, GL_DEPTH_COMPONENT24, size.width(), size.height());
+        m_context->framebufferRenderbuffer(GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT, GL_RENDERBUFFER, m_depthBuffer);
+    } else if (m_packedDepthStencilExtensionSupported) {
         if (!m_depthStencilBuffer)
             m_depthStencilBuffer = m_context->createRenderbuffer();
         m_context->bindRenderbuffer(GL_RENDERBUFFER, m_depthStencilBuffer);
         if (m_antiAliasingMode == MSAAImplicitResolve)
             m_context->renderbufferStorageMultisampleEXT(GL_RENDERBUFFER, m_sampleCount, GL_DEPTH24_STENCIL8_OES, size.width(), size.height());
         else if (m_antiAliasingMode == MSAAExplicitResolve)
             m_context->renderbufferStorageMultisampleCHROMIUM(GL_RENDERBUFFER, m_sampleCount, GL_DEPTH24_STENCIL8_OES, size.width(), size.height());
         else
             m_context->renderbufferStorage(GL_RENDERBUFFER, GL_DEPTH24_STENCIL8_OES, size.width(), size.height());
         m_context->framebufferRenderbuffer(GL_FRAMEBUFFER, GL_DEPTH_STENCIL_ATTACHMENT, GL_RENDERBUFFER, m_depthStencilBuffer);
@@ skipping 355 matching lines @@
 
     if (m_antiAliasingMode == MSAAImplicitResolve)
         m_context->framebufferTexture2DMultisampleEXT(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, target, m_colorBuffer.textureId, 0, m_sampleCount);
     else
         m_context->framebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, target, m_colorBuffer.textureId, 0);
 
     m_context->bindTexture(GL_TEXTURE_2D, m_texture2DBinding);
 }
 
 } // namespace blink