Fix bug in texture usage mask.

Author: chinmaygarde

impeller/playground/playground.mm

@@ -162,8 +162,7 @@ static void PlaygroundKeyCallback(GLFWwindow* window,
     stencil0_tex.format = PixelFormat::kD32FloatS8UNormInt;
     stencil0_tex.size = color0_tex.size;
     stencil0_tex.usage =
-        static_cast<TextureUsageMask>(TextureUsage::kShaderRead) |
-        static_cast<TextureUsageMask>(TextureUsage::kShaderWrite);
+        static_cast<TextureUsageMask>(TextureUsage::kRenderTarget);
     auto stencil_texture =
         renderer_.GetContext()->GetPermanentsAllocator()->CreateTexture(
             StorageMode::kDeviceTransient, stencil0_tex);

impeller/renderer/formats.h

@@ -94,10 +94,10 @@ enum class StoreAction {
 using TextureUsageMask = uint64_t;
 
 enum class TextureUsage : TextureUsageMask {
-  kUnknown,
-  kShaderRead,
-  kShaderWrite,
-  kRenderTarget,
+  kUnknown = 0,
+  kShaderRead = 1 << 0,
+  kShaderWrite = 1 << 1,
+  kRenderTarget = 1 << 2,
 };
 
 enum class WindingOrder {

impeller/renderer/render_target.cc

@@ -84,8 +84,7 @@ RenderTarget RenderTarget::CreateOffscreen(const Context& context,
   stencil_tex0.format = PixelFormat::kD32FloatS8UNormInt;
   stencil_tex0.size = size;
   stencil_tex0.usage =
-      static_cast<TextureUsageMask>(TextureUsage::kShaderRead) |
-      static_cast<TextureUsageMask>(TextureUsage::kShaderWrite);
+      static_cast<TextureUsageMask>(TextureUsage::kRenderTarget);
 
   ColorAttachment color0;
   color0.clear_color = Color::BlackTransparent();