webgl: use immutable texture for the default FBO.

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 133 matching lines @@
     , m_drawFramebufferBinding(0)
     , m_readFramebufferBinding(0)
     , m_activeTextureUnit(GL_TEXTURE0)
     , m_context(context)
     , m_extensionsUtil(extensionsUtil)
     , m_size(-1, -1)
     , m_requestedAttributes(requestedAttributes)
     , m_multisampleExtensionSupported(multisampleExtensionSupported)
     , m_packedDepthStencilExtensionSupported(packedDepthStencilExtensionSupported)
     , m_discardFramebufferSupported(discardFramebufferSupported)
+    , m_storageTextureSupported(false)
     , 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 102 matching lines @@
         WebGLImageConversion::AlphaOp op = needPremultiply ? WebGLImageConversion::AlphaDoPremultiply : WebGLImageConversion::AlphaDoNothing;
         if (pixels)
             readBackFramebuffer(pixels, size().width(), size().height(), ReadbackSkia, op);
     }
 
     // We must restore the texture binding since creating new textures,
     // consuming and producing mailboxes changes it.
     ScopedTextureUnit0BindingRestorer restorer(m_context.get(), m_activeTextureUnit, m_texture2DBinding);
 
     // First try to recycle an old buffer.
     RefPtr<MailboxInfo> frontColorBufferMailbox = recycledMailbox();

[dshwang, 2015/11/20 09:31:32]

resizing code is here. it calls allocateTextureMemory() eventually and resizes
mailbox texture.

[Ken Russell (switch to Gerrit), 2015/11/23 22:26:31]

OK, thanks, I had missed the fact that recycledMailbox() checked the size of the
texture associated with the recycled mailbox.

 
     // No buffer available to recycle, create a new one.
     if (!frontColorBufferMailbox) {
         TextureInfo newTexture;
         newTexture.textureId = createColorTexture();
         allocateTextureMemory(&newTexture, m_size);
         // Bad things happened, abandon ship.
         if (!newTexture.textureId)
             return false;
 
@@ skipping 11 matching lines @@
             m_context->framebufferTexture2DMultisampleEXT(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, m_colorBuffer.textureId, 0, m_sampleCount);
         else
             m_context->framebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, m_colorBuffer.textureId, 0);
 
         if (m_discardFramebufferSupported) {
             // Explicitly discard framebuffer to save GPU memory bandwidth for tile-based GPU arch.
             const WGC3Denum attachments[3] = { GL_COLOR_ATTACHMENT0, GL_DEPTH_ATTACHMENT, GL_STENCIL_ATTACHMENT};
             m_context->discardFramebufferEXT(GL_FRAMEBUFFER, 3, attachments);
         }
     } else {
-        m_context->copyTextureCHROMIUM(GL_TEXTURE_2D, m_colorBuffer.textureId, frontColorBufferMailbox->textureInfo.textureId, GL_RGBA, GL_UNSIGNED_BYTE, GL_FALSE, GL_FALSE, GL_FALSE);
+        m_context->copySubTextureCHROMIUM(GL_TEXTURE_2D, m_colorBuffer.textureId, frontColorBufferMailbox->textureInfo.textureId,

[dshwang, 2015/11/19 12:33:00]

copyTextureCHROMIUM must not used for immutable texture as target, because it
can redefine the texture.

[Ken Russell (switch to Gerrit), 2015/11/19 21:47:41]

If this code was relying on the copyTextureCHROMIUM call to resize the texture
in the mailbox, then what's doing the same when the canvas is resized now? It
looks to me like this introduces a bug when preserveDrawingBuffer=true and the
canvas is resized, since nobody clears out the recycled mailboxes. I think you
can catch the bug by drawing to a 128x128 canvas, resizing it larger (to
256x256), re-rendering so that a different color is drawn for fragments with x
or y > 128, and reading back the lower-right corner to verify the canvas was
resized correctly. Can you please write such a test and verify that it passes?
Especially if it doesn't, could you submit a pull request to
https://github.com/KhronosGroup/WebGL under either conformance/context or
conformance/canvas adding one?

[dshwang, 2015/11/20 09:31:32]

This code doesn't rely on copyTextureCHROMIUM call to resize the texture.
copyTextureCHROMIUM emits GL_INVALID_OPERATION if the target texture is
immutable.
https://code.google.com/p/chromium/codesearch#chromium/src/gpu/command_buffer...

As this CL changes target texture to immutable, we can not use
copyTextureCHROMIUM. the source and target texture always existsm so we can use
copySubTextureCHROMIUM.

On the other hands, the test idea is good. 
WebglConformance.conformance_textures_webgl_canvas_tex_image_and_sub_image_2d_with_webgl_canvas_*
covers what you explain in discard case.
If you still think the test is needed, let me extend
WebglConformance.conformance_textures_webgl_canvas_tex_image_and_sub_image_2d_with_webgl_canvas_*
or WebglConformance.conformance_textures_misc_texture_size.

[Ken Russell (switch to Gerrit), 2015/11/23 22:26:31]

I went ahead and wrote the test I had in mind in
https://github.com/KhronosGroup/WebGL/pull/1325 . Please verify that this test
continues to pass with your CL. We should roll forward the WebGL conformance
tests to pick this up.

[dshwang, 2015/11/24 12:05:11]

Thank you for adding test! The test works well with this CL. In addition, I
checked the test cover this code path.

+            0, 0, 0, 0, m_size.width(), m_size.height(), GL_FALSE, GL_FALSE, GL_FALSE);
     }
 
     restoreFramebufferBindings();
     m_contentsChanged = false;
 
     m_context->produceTextureDirectCHROMIUM(frontColorBufferMailbox->textureInfo.textureId, GL_TEXTURE_2D, frontColorBufferMailbox->mailbox.name);
     m_context->flush();
     frontColorBufferMailbox->mailbox.validSyncToken = m_context->insertSyncPoint(frontColorBufferMailbox->mailbox.syncToken);
     frontColorBufferMailbox->mailbox.allowOverlay = frontColorBufferMailbox->textureInfo.imageId != 0;
     setBufferClearNeeded(true);
@@ skipping 123 matching lines @@
     if (m_requestedAttributes.antialias && m_multisampleExtensionSupported) {
         m_context->getIntegerv(GL_MAX_SAMPLES_ANGLE, &maxSampleCount);
         m_antiAliasingMode = MSAAExplicitResolve;
         if (m_extensionsUtil->supportsExtension("GL_EXT_multisampled_render_to_texture")) {
             m_antiAliasingMode = MSAAImplicitResolve;
         } else if (m_extensionsUtil->supportsExtension("GL_CHROMIUM_screen_space_antialiasing")) {
             m_antiAliasingMode = ScreenSpaceAntialiasing;
         }
     }
     m_sampleCount = std::min(4, maxSampleCount);
+    m_storageTextureSupported = m_extensionsUtil->supportsExtension("GL_EXT_texture_storage");
 
     m_fbo = m_context->createFramebuffer();
 
     m_context->bindFramebuffer(GL_FRAMEBUFFER, m_fbo);
     m_colorBuffer.textureId = createColorTexture();
     if (m_antiAliasingMode == MSAAImplicitResolve)
         m_context->framebufferTexture2DMultisampleEXT(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, m_colorBuffer.textureId, 0, m_sampleCount);
     else
         m_context->framebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, m_colorBuffer.textureId, 0);
     createSecondaryBuffers();
@@ skipping 490 matching lines @@
     unsigned count = height / 2;
     for (unsigned i = 0; i < count; i++) {
         uint8* rowA = framebuffer + i * rowBytes;
         uint8* rowB = framebuffer + (height - i - 1) * rowBytes;
         memcpy(scanline, rowB, rowBytes);
         memcpy(rowB, rowA, rowBytes);
         memcpy(rowA, scanline, rowBytes);
     }
 }
 
-void DrawingBuffer::texImage2DResourceSafe(GLenum target, GLint level, GLenum internalformat, GLsizei width, GLsizei height, GLint border, GLenum format, GLenum type, GLint unpackAlignment)
-{
-    ASSERT(unpackAlignment == 1 || unpackAlignment == 2 || unpackAlignment == 4 || unpackAlignment == 8);
-    m_context->texImage2D(target, level, internalformat, width, height, border, format, type, 0);
-}
-
 void DrawingBuffer::allocateTextureMemory(TextureInfo* info, const IntSize& size)
 {
     if (RuntimeEnabledFeatures::webGLImageChromiumEnabled()) {
         deleteChromiumImageForTexture(info);
 
         info->imageId = m_context->createGpuMemoryBufferImageCHROMIUM(size.width(), size.height(), GL_RGBA, GC3D_SCANOUT_CHROMIUM);
         if (info->imageId) {
             m_context->bindTexImage2DCHROMIUM(GL_TEXTURE_2D, info->imageId);
             return;
         }
     }
 
-    texImage2DResourceSafe(GL_TEXTURE_2D, 0, m_internalColorFormat, size.width(), size.height(), 0, m_colorFormat, GL_UNSIGNED_BYTE);
+    if (m_storageTextureSupported) {
+        if (info->immutable) {
+            m_context->deleteTexture(info->textureId);
+            info->textureId = createColorTexture();
+        }
+
+        // TODO(dshwang): GL_BGRA8_EXT can be better in some platforms. crbug.com/557848
+        m_context->texStorage2DEXT(GL_TEXTURE_2D, 1, m_internalRenderbufferFormat, size.width(), size.height());
+        info->immutable = true;
+        return;
+    }
+    m_context->texImage2D(GL_TEXTURE_2D, 0, m_internalColorFormat, size.width(), size.height(), 0, m_colorFormat, GL_UNSIGNED_BYTE, 0);
 }
 
 void DrawingBuffer::deleteChromiumImageForTexture(TextureInfo* info)
 {
     if (info->imageId) {
         m_context->releaseTexImage2DCHROMIUM(GL_TEXTURE_2D, info->imageId);
         m_context->destroyImageCHROMIUM(info->imageId);
         info->imageId = 0;
     }
 }
 
 } // namespace blink