Implement support for mixed sampled render targets

include/gpu/GrTypes.h

Index: include/gpu/GrTypes.h
diff --git a/include/gpu/GrTypes.h b/include/gpu/GrTypes.h
index fc233ea0cdf60646c49261f3c326b58e2d40d7aa..16d0db225557b2d50b3c7353e7a80f0517124f72 100644
--- a/include/gpu/GrTypes.h
+++ b/include/gpu/GrTypes.h
@@ -530,6 +530,21 @@ struct GrBackendTextureDesc {
 ///////////////////////////////////////////////////////////////////////////////
 
 /**
+ * Optional bitfield flags that can be set on GrBackendRenderTargetDesc (below).
+ */
+enum GrBackendRenderTargetFlags {

[bsalomon, 2015/06/10 19:57:06]

I'm wondering if it is necessary to extend wrapped render targets to support
mixed samples.

Wrapped RTs are generally less useful than wrapped textures because they can
never be as a source for a draw. It really only exists for wrapping FBO 0. Our
clients typically don't use this but instead have Skia create a texture to
render to or they provide Skia a texture ID and we create the FBO and stencil
buffers to pair with it.

Is it possible for FBO 0 to be mixed?

If there is a client for this, could we have separate stencil/color sample
counts in the descriptor and simply fail if the combo is illegal?

[Chris Dalton, 2015/06/10 20:55:56]

Mixed samples is not supported for FBO 0 so we can just take this out. It just
won't be possible to wrap a mixed render target, which is fine.

+    kNone_GrBackendRenderTargetFlags            = 0x0,
+    /**
+     * Which buffers are multisampled (color and stencil, or just stencil?).
+     * The default is both. Note that mixing multisampled and aliased buffers
+     * is only possible if NV_framebuffer_mixed_samples is available.
+     */
+    kStencilMSAAOnly_GrBackendRenderTargetFlags = 0x1,
+};
+
+GR_MAKE_BITFIELD_OPS(GrBackendRenderTargetFlags)
+
+/**
  * Gr can wrap an existing render target created by the client in the 3D API
  * with a GrRenderTarget object. The client is responsible for ensuring that the
  * underlying 3D API object lives at least as long as the GrRenderTarget object
@@ -541,6 +556,7 @@ struct GrBackendTextureDesc {
 
 struct GrBackendRenderTargetDesc {
     GrBackendRenderTargetDesc() { memset(this, 0, sizeof(*this)); }
+    GrBackendRenderTargetFlags      fFlags;
     int                             fWidth;         //<! width in pixels
     int                             fHeight;        //<! height in pixels
     GrPixelConfig                   fConfig;        //<! color format