wgpu: Stub out more blend modes

render/wgpu/src/pipelines.rs

@@ -59,23 +59,131 @@ impl ShapePipeline {
 }
 
 fn blend_mode_to_state(mode: BlendMode) -> Option<wgpu::BlendState> {
+    // Use the GPU blend modes to roughly approximate Flash's blend modes.
+    // This should look reasonable for the most common cases, but full support requires
+    // rendering to an intermediate texture and custom shaders for the complex blend modes.
     match mode {
         BlendMode::Normal => Some(wgpu::BlendState::PREMULTIPLIED_ALPHA_BLENDING),
-        BlendMode::Add => {
+
+        // TODO: Needs intermediate buffer.
+        BlendMode::Layer => Some(wgpu::BlendState::PREMULTIPLIED_ALPHA_BLENDING),
+
+        // dst * src
+        BlendMode::Multiply => Some(wgpu::BlendState {
+            color: wgpu::BlendComponent {
+                src_factor: wgpu::BlendFactor::Dst,
+                dst_factor: wgpu::BlendFactor::Zero,
+                operation: wgpu::BlendOperation::Add,
+            },
+            alpha: wgpu::BlendComponent::OVER,
+        }),
+
+        // 1 - (1 - dst) * (1 - src)
+        // TODO: Needs shader. Rendererd as additive for now.
+        BlendMode::Screen => Some(wgpu::BlendState {
+            color: wgpu::BlendComponent {
+                src_factor: wgpu::BlendFactor::One,
+                dst_factor: wgpu::BlendFactor::One,
+                operation: wgpu::BlendOperation::Add,
+            },
+            alpha: wgpu::BlendComponent::OVER,
+        }),
+
+        // max(dst, src)
+        BlendMode::Lighten => Some(wgpu::BlendState {
+            color: wgpu::BlendComponent {
+                src_factor: wgpu::BlendFactor::One,
+                dst_factor: wgpu::BlendFactor::One,
+                operation: wgpu::BlendOperation::Max,
+            },
+            alpha: wgpu::BlendComponent::OVER,
+        }),
+
+        // min(dst, src)
+        BlendMode::Darken => Some(wgpu::BlendState {
+            color: wgpu::BlendComponent {
+                src_factor: wgpu::BlendFactor::One,
+                dst_factor: wgpu::BlendFactor::One,
+                operation: wgpu::BlendOperation::Min,
+            },
+            alpha: wgpu::BlendComponent::OVER,
+        }),
+
+        // abs(dst - src)
+        // TODO: Needs shader. Rendererd as subtract for now.
+        BlendMode::Difference => {
             Some(wgpu::BlendState {
                 // Add src and dst RGB values together
                 color: wgpu::BlendComponent {
                     src_factor: wgpu::BlendFactor::One,
                     dst_factor: wgpu::BlendFactor::One,
-                    operation: wgpu::BlendOperation::Add,
+                    operation: wgpu::BlendOperation::ReverseSubtract,
                 },
                 alpha: wgpu::BlendComponent::OVER,
             })
         }
-        _ => {
+
-            log::warn!("Webgpu backend does not yet support blend mode {:?}", mode);
+        // dst + src
-            Some(wgpu::BlendState::PREMULTIPLIED_ALPHA_BLENDING)
+        BlendMode::Add => Some(wgpu::BlendState {
-        }
+            color: wgpu::BlendComponent {
+                src_factor: wgpu::BlendFactor::One,
+                dst_factor: wgpu::BlendFactor::One,
+                operation: wgpu::BlendOperation::Add,
+            },
+            alpha: wgpu::BlendComponent::OVER,
+        }),
+
+        // dst - src
+        BlendMode::Subtract => Some(wgpu::BlendState {
+            color: wgpu::BlendComponent {
+                src_factor: wgpu::BlendFactor::One,
+                dst_factor: wgpu::BlendFactor::One,
+                operation: wgpu::BlendOperation::ReverseSubtract,
+            },
+            alpha: wgpu::BlendComponent::OVER,
+        }),
+
+        // 1 - dst
+        BlendMode::Invert => Some(wgpu::BlendState {
+            color: wgpu::BlendComponent {
+                src_factor: wgpu::BlendFactor::Zero,
+                dst_factor: wgpu::BlendFactor::OneMinusDst,
+                operation: wgpu::BlendOperation::Add,
+            },
+            alpha: wgpu::BlendComponent::OVER,
+        }),
+
+        // TODO: Requires intermediate buffer.
+        // dst.alpha = src.alpha
+        // Parent display object needs to have Layer blend mode.
+        BlendMode::Alpha => Some(wgpu::BlendState::PREMULTIPLIED_ALPHA_BLENDING),
+
+        // TODO: Requires intermediate buffer.
+        // dst.alpha = 1 - src.alpha
+        // Parent display object needs to have Layer blend mode.
+        BlendMode::Erase => Some(wgpu::BlendState::PREMULTIPLIED_ALPHA_BLENDING),
+
+        // if src > .5 { 1 - (1 - dst) * (1 - src) } else { dst * src }
+        // TODO: Needs shader, rendered as multiply for now.
+        BlendMode::HardLight => Some(wgpu::BlendState {
+            color: wgpu::BlendComponent {
+                src_factor: wgpu::BlendFactor::Dst,
+                dst_factor: wgpu::BlendFactor::Zero,
+                operation: wgpu::BlendOperation::Add,
+            },
+            alpha: wgpu::BlendComponent::OVER,
+        }),
+
+        // if dst > .5 { 1 - (1 - dst) * (1 - src) } else { dst * src }
+        // TODO: Needs shader, rendered as multiply for now.
+        BlendMode::Overlay => Some(wgpu::BlendState {
+            color: wgpu::BlendComponent {
+                src_factor: wgpu::BlendFactor::Dst,
+                dst_factor: wgpu::BlendFactor::Zero,
+                operation: wgpu::BlendOperation::Add,
+            },
+            alpha: wgpu::BlendComponent::OVER,
+        }),
     }
 }