feat: embed eraser stroke into stroke texture

Memola/Canvas/Core/Renderer.swift

@@ -69,6 +69,7 @@ final class Renderer {
 
     func draw(in view: MTKView, on canvas: Canvas) {
         if !updatesViewPort {
+            strokeRenderPass.eraserRenderPass = eraserRenderPass
             graphicRenderPass.photoRenderPass = photoRenderPass
             graphicRenderPass.strokeRenderPass = strokeRenderPass
             graphicRenderPass.eraserRenderPass = eraserRenderPass

Memola/Canvas/RenderPasses/GraphicRenderPass.swift

@@ -67,13 +67,6 @@ class GraphicRenderPass: RenderPass {
                         strokeRenderPass.graphicDescriptor = descriptor
                         strokeRenderPass.graphicPipelineState = graphicPipelineState
                         strokeRenderPass.draw(on: canvas, with: renderer)
-
-                        if let stroke = stroke as? PenStroke, !stroke.isEmptyErasedQuads {
-                            descriptor.colorAttachments[0].loadAction = .load
-                            eraserRenderPass.stroke = stroke
-                            eraserRenderPass.descriptor = descriptor
-                            eraserRenderPass.draw(on: canvas, with: renderer)
-                        }
                     }
                 case .photo(let photo):
                     descriptor.colorAttachments[0].loadAction = clearsTexture ? .clear : .load
@@ -103,13 +96,6 @@ class GraphicRenderPass: RenderPass {
                     strokeRenderPass.graphicDescriptor = descriptor
                     strokeRenderPass.graphicPipelineState = graphicPipelineState
                     strokeRenderPass.draw(on: canvas, with: renderer)
-
-                    if let stroke = stroke as? PenStroke, !stroke.isEmptyErasedQuads {
-                        descriptor.colorAttachments[0].loadAction = .load
-                        eraserRenderPass.stroke = stroke
-                        eraserRenderPass.descriptor = descriptor
-                        eraserRenderPass.draw(on: canvas, with: renderer)
-                    }
                 }
             case .photo(let photo):
                 photoRenderPass.photo = photo

Memola/Canvas/RenderPasses/StrokeRenderPass.swift

@@ -21,6 +21,8 @@ class StrokeRenderPass: RenderPass {
     var stroke: (any Stroke)?
     var strokeTexture: MTLTexture?
 
+    weak var eraserRenderPass: EraserRenderPass?
+
     init(renderer: Renderer) {
         descriptor = MTLRenderPassDescriptor()
         strokePipelineState = PipelineStates.createStrokePipelineState(from: renderer)
@@ -57,6 +59,13 @@ class StrokeRenderPass: RenderPass {
         renderEncoder.endEncoding()
         commandBuffer.commit()
 
+        if let eraserRenderPass, let stroke = stroke as? PenStroke, !stroke.isEmptyErasedQuads {
+            descriptor.colorAttachments[0].loadAction = .load
+            eraserRenderPass.stroke = stroke
+            eraserRenderPass.descriptor = descriptor
+            eraserRenderPass.draw(on: canvas, with: renderer)
+        }
+
         drawStrokeTexture(on: canvas, with: renderer)
     }