Fix vulkan image sampling

src/gpu/vk/GrVkGpu.cpp

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "GrVkGpu.h"
 
 #include "GrContextOptions.h"
@@ skipping 766 matching lines @@
 
     // We cannot generate mipmaps for images that are multisampled.
     // TODO: does it even make sense for rendertargets in general?
     if (tex->asRenderTarget() && tex->asRenderTarget()->numColorSamples() > 1) {
         return;
     }
 
     // determine if we can blit to and from this format
     const GrVkCaps& caps = this->vkCaps();
     if (!caps.configCanBeDstofBlit(tex->config(), false) ||
-        !caps.configCanBeSrcofBlit(tex->config(), false)) {
+        !caps.configCanBeSrcofBlit(tex->config(), false) ||
+        !caps.mipMapSupport()) {
         return;
     }

[egdaniel, 2016/07/01 20:20:22]

On Nvidia, there seems to be a driver bug in blitting to create the mip maps. We
can land this CL as is which will occasionally draw corrupted triangles on on
parts of images we've mipmaped. This does not repro on the 5X. A work around
that seems to work is simply submitting the current command buffer here (doens't
need a sync) before blitting. We can wrap this is some cap that is set on Nvidia
only (but then we may not notice if their driver fixes it).

[bsalomon, 2016/07/02 00:50:12]

I leave it to you whether you want to workaround the bug or not. It'd be a good
to submit a bug to NV so they can fix it. Then we'd also probably know when to
remove the workaround after the fix.

[jvanverth1, 2016/07/06 15:19:42]

I'm fine with landing this as is, and creating a separate patch that submits the
command buffer.

 
     // change the original image's layout
     tex->setImageLayout(this, VK_IMAGE_LAYOUT_TRANSFER_SRC_OPTIMAL,
                         VK_ACCESS_TRANSFER_READ_BIT, VK_PIPELINE_STAGE_TRANSFER_BIT, false);
 
     // grab handle to the original image resource
     const GrVkResource* oldResource = tex->resource();
     oldResource->ref();
     VkImage oldImage = tex->image();
 
@@ skipping 709 matching lines @@
     }
 
     // Currently it is fine for us to always pass in 1 for the clear count even if no attachment
     // uses it. In the current state, we also only use the LOAD_OP_CLEAR for the color attachment
     // which is always at the first attachment.
     fCurrentCmdBuffer->beginRenderPass(this, renderPass, 1, colorClear, *target, *pBounds, true);
     fCurrentCmdBuffer->executeCommands(this, buffer);
     fCurrentCmdBuffer->endRenderPass(this);
 }