Improve drawing error messages

wgpu-core/src/command/render.rs

@@ -29,7 +29,7 @@ use wgt::{
     TextureUsage, BIND_BUFFER_ALIGNMENT,
 };
 
-use std::{borrow::Borrow, collections::hash_map::Entry, iter, mem, ops::Range, slice};
+use std::{borrow::Borrow, collections::hash_map::Entry, fmt, iter, mem, ops::Range, slice};
 
 pub type RenderPassColorAttachmentDescriptor =
     RenderPassColorAttachmentDescriptorBase<id::TextureViewId>;
@@ -174,7 +174,7 @@ impl OptionalState {
     }
 }
 
-#[derive(Debug, PartialEq)]
+#[derive(PartialEq)]
 enum DrawError {
     MissingBlendColor,
     MissingStencilReference,
@@ -186,6 +186,17 @@ enum DrawError {
     },
 }
 
+impl fmt::Debug for DrawError {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            DrawError::MissingBlendColor => write!(f, "MissingBlendColor. A blend color is required to be set using RenderPass::set_blend_color."),
+            DrawError::MissingStencilReference => write!(f, "MissingStencilReference. A stencil reference is required to be set using RenderPass::set_stencil_reference."),
+            DrawError::MissingPipeline => write!(f, "MissingPipeline. You must first set the render pipeline using RenderPass::set_pipeline."),
+            DrawError::IncompatibleBindGroup { index } => write!(f, "IncompatibleBindGroup. The current render pipeline has a layout which is incompatible with a currently set bind group. They first differ at entry index {}.", index),
+        }
+    }
+}
+
 #[derive(Debug)]
 pub struct IndexState {
     bound_buffer_view: Option<(id::BufferId, Range<BufferAddress>)>,