WIP on creating utils for creating offscreen render targets.

Author: chinmaygarde

impeller/playground/playground.mm

@@ -144,28 +144,29 @@ static void PlaygroundKeyCallback(GLFWwindow* window,
       return false;
     }
 
-    TextureDescriptor color0_desc;
-    color0_desc.format = PixelFormat::kB8G8R8A8UNormInt;
-    color0_desc.size = {
+    TextureDescriptor color0_tex;
+    color0_tex.format = PixelFormat::kB8G8R8A8UNormInt;
+    color0_tex.size = {
         static_cast<ISize::Type>(current_drawable.texture.width),
         static_cast<ISize::Type>(current_drawable.texture.height)};
+    color0_tex.usage = static_cast<uint64_t>(TextureUsage::kRenderTarget);
 
     ColorAttachment color0;
     color0.texture =
-        std::make_shared<TextureMTL>(color0_desc, current_drawable.texture);
+        std::make_shared<TextureMTL>(color0_tex, current_drawable.texture);
     color0.clear_color = Color::SkyBlue();
     color0.load_action = LoadAction::kClear;
     color0.store_action = StoreAction::kStore;
 
-    TextureDescriptor stencil_texture_descriptor;
-    stencil_texture_descriptor.format = PixelFormat::kD32FloatS8UNormInt;
-    stencil_texture_descriptor.size = color0_desc.size;
-    stencil_texture_descriptor.usage =
+    TextureDescriptor stencil0_tex;
+    stencil0_tex.format = PixelFormat::kD32FloatS8UNormInt;
+    stencil0_tex.size = color0_tex.size;
+    stencil0_tex.usage =
         static_cast<TextureUsageMask>(TextureUsage::kShaderRead) |
         static_cast<TextureUsageMask>(TextureUsage::kShaderWrite);
     auto stencil_texture =
         renderer_.GetContext()->GetPermanentsAllocator()->CreateTexture(
-            StorageMode::kDeviceTransient, stencil_texture_descriptor);
+            StorageMode::kDeviceTransient, stencil0_tex);
     stencil_texture->SetLabel("PlaygroundMainStencil");
 
     StencilAttachment stencil0;

impeller/renderer/backend/metal/render_pass_mtl.mm

@@ -114,6 +114,9 @@ static bool ConfigureStencilAttachment(
 }
 
 void RenderPassMTL::SetLabel(std::string label) {
+  if (label.empty()) {
+    return;
+  }
   label_ = std::move(label);
   transients_buffer_->SetLabel(SPrintF("%s Transients", label_.c_str()));
 }

impeller/renderer/render_target.cc

@@ -4,6 +4,8 @@
 
 #include "impeller/renderer/render_target.h"
 
+#include "impeller/renderer/allocator.h"
+#include "impeller/renderer/context.h"
 #include "impeller/renderer/texture.h"
 
 namespace impeller {
@@ -70,4 +72,52 @@ const std::optional<StencilAttachment>& RenderTarget::GetStencilAttachment()
   return stencil_;
 }
 
+RenderTarget RenderTarget::CreateOffscreen(const Context& context,
+                                           ISize size,
+                                           std::string label) {
+  TextureDescriptor color_tex0;
+  color_tex0.format = PixelFormat::kB8G8R8A8UNormInt;
+  color_tex0.size = size;
+  color_tex0.usage = static_cast<uint64_t>(TextureUsage::kRenderTarget);
+
+  TextureDescriptor stencil_tex0;
+  stencil_tex0.format = PixelFormat::kD32FloatS8UNormInt;
+  stencil_tex0.size = size;
+  stencil_tex0.usage =
+      static_cast<TextureUsageMask>(TextureUsage::kShaderRead) |
+      static_cast<TextureUsageMask>(TextureUsage::kShaderWrite);
+
+  ColorAttachment color0;
+  color0.clear_color = Color::BlackTransparent();
+  color0.load_action = LoadAction::kClear;
+  color0.store_action = StoreAction::kStore;
+  color0.texture = context.GetPermanentsAllocator()->CreateTexture(
+      StorageMode::kDevicePrivate, color_tex0);
+
+  if (!color0.texture) {
+    return {};
+  }
+
+  color0.texture->SetLabel(label);
+
+  StencilAttachment stencil0;
+  stencil0.load_action = LoadAction::kClear;
+  stencil0.store_action = StoreAction::kDontCare;
+  stencil0.clear_stencil = 0u;
+  stencil0.texture = context.GetPermanentsAllocator()->CreateTexture(
+      StorageMode::kDeviceTransient, stencil_tex0);
+
+  if (!stencil0.texture) {
+    return {};
+  }
+
+  stencil0.texture->SetLabel(label);
+
+  RenderTarget target;
+  target.SetColorAttachment(std::move(color0), 0u);
+  target.SetStencilAttachment(std::move(stencil0));
+
+  return target;
+}
+
 }  // namespace impeller

impeller/renderer/render_target.h

@@ -13,8 +13,14 @@
 
 namespace impeller {
 
+class Context;
+
 class RenderTarget {
  public:
+  static RenderTarget CreateOffscreen(const Context& context,
+                                      ISize size,
+                                      std::string label = "Offscreen");
+
   RenderTarget();
 
   ~RenderTarget();