Orgnaization & cleanup

draw/shaders/source/backdrop_blur.vert

@@ -1,18 +1,19 @@
 #version 450 core
 
 // Unified backdrop blur vertex shader.
-// Handles both H-blur (fullscreen triangle, mode 0) and V-blur+composite (instanced
-// unit-quad over Backdrop_Primitive storage buffer, mode 1) for the second PSO of
-// the backdrop bracket. The first PSO (downsample) uses backdrop_fullscreen.vert.
+// Handles both the 1D separable blur passes (fullscreen triangle, mode 0; used for
+// BOTH the H-pass and V-pass) and the composite pass (instanced unit-quad over
+// Backdrop_Primitive storage buffer, mode 1) for the second PSO of the backdrop bracket.
+// The first PSO (downsample) uses backdrop_fullscreen.vert.
 //
 // No vertex buffer for either mode. Mode 0 uses gl_VertexIndex 0..2 for a single
 // fullscreen triangle; mode 1 uses gl_VertexIndex 0..5 for a unit-quad (two
 // triangles, TRIANGLELIST topology) and gl_InstanceIndex to select the primitive.
 //
-// Mode 0 viewport+scissor are CPU-set per layer-bracket to the work region (union
-// AABB of backdrop primitives + 3*max_sigma, clamped to swapchain bounds). Mode 1
-// renders into the main render target with the screen-space orthographic projection;
-// the per-primitive bounds drive the quad in screen space.
+// Mode 0 viewport+scissor are CPU-set per sigma group to the work region (union AABB
+// of that group's backdrop primitives + halo, clamped to swapchain bounds). Mode 1
+// renders into source_texture with the screen-space orthographic projection; the
+// per-primitive bounds drive the quad in screen space.
 //
 // Backdrop primitives have NO rotation — backdrop sampling is in screen space, so
 // a rotated mask over a stationary blur sample would look wrong.
@@ -46,11 +47,11 @@ layout(set = 1, binding = 0) uniform Uniforms {
 // vec2 and scalar tail packs tight to land the struct at a clean 48-byte
 // stride (a multiple of 16, so the array stride needs no rounding either).
 // Field semantics match the CPU-side Backdrop_Primitive declared in
-// levlib/draw/pipeline_2d_backdrop.odin; keep both in sync.
+// levlib/draw/backdrop.odin; keep both in sync.
 //
-// Backdrop primitives are tint-only in v1: outline is intentionally absent.
-// Future specialized effects (e.g. liquid-glass-style edges) would be a
-// dedicated primitive type with its own pipeline rather than a flag bit here.
+// Backdrop primitives are tint-only: outline is intentionally absent. Specialized
+// edge effects (e.g. liquid-glass-style refraction outlines) would be a dedicated
+// primitive type with its own pipeline rather than a flag bit here.
 struct Backdrop_Primitive {
     vec4 bounds; //  0-15: min_xy, max_xy (world-space)
     vec4 radii; // 16-31: per-corner radii (physical px)