Orgnaization & cleanup
This commit is contained in:
Zachary Levy
+33
-32
@@ -21,16 +21,16 @@ import sdl "vendor:sdl3"
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// sigma_phys ≤ 8 → factor = 2
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// sigma_phys > 8 → factor = 4 (capped)
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//
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// Capped at factor=4: master's preference for visual quality over bandwidth at the high end.
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// Larger factors (8 and 16) would lose more high-frequency detail than the kernel can mask
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// even with the H+V split, and the bandwidth saving is small (the work region also shrinks
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// quadratically, so most of the savings are already captured at factor=4).
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// Capped at factor=4 to favor visual quality over bandwidth at the high end. Larger factors
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// (8 and 16) would lose more high-frequency detail than the kernel can mask even with the
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// H+V split, and the bandwidth saving is small (the work region also shrinks quadratically,
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// so most of the savings are already captured at factor=4).
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//
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// Working textures are sized at full swapchain resolution to support factor=1. Larger factors
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// just write to a smaller sub-rect via viewport-limited rendering. Memory cost: ½-res → full-
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// res working textures means 4× more bytes per working texture (2 textures, RGBA8: roughly
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// 16 MB at 1080p, 64 MB at 4K). On modern GPUs this is well within budget; on Mali Valhall
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// SBCs it's negligible against unified-memory headroom.
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// just write to a smaller sub-rect via viewport-limited rendering. Memory cost: full-res
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// working textures (2 textures, RGBA8) is roughly 16 MB at 1080p, 64 MB at 4K. On modern
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// GPUs this is well within budget; on Mali Valhall SBCs it's negligible against unified-
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// memory headroom.
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//
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// The shaders read the factor as a uniform. The downsample shader has three paths (factor=1
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// identity, factor=2 single bilinear tap, factor>=4 four bilinear taps with offsets scaling
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@@ -86,7 +86,7 @@ Backdrop_Vert_Uniforms :: struct {
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// shaders/source/backdrop_downsample.frag.
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Backdrop_Downsample_Frag_Uniforms :: struct {
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inv_source_size: [2]f32, // 0: 8 — 1.0 / source_texture pixel dimensions (full-res)
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downsample_factor: u32, // 8: 4 — 2 or 4 (selects 1-tap vs 4-tap path in shader)
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downsample_factor: u32, // 8: 4 — 1, 2, or 4 (selects identity / 1-tap / 4-tap path in shader)
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_pad0: u32, // 12: 4
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}
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@@ -120,11 +120,12 @@ Pipeline_2D_Backdrop :: struct {
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primitive_buffer: Buffer,
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// Working textures, allocated once at swapchain resolution and recreated only on resize.
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// `source_texture` is full-resolution; the other two are ¼-res. All single-sample.
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// All three are sized at full swapchain resolution and single-sample. Larger downsample
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// factors fill only a sub-rect via viewport-limited rendering (see file-header comment).
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// source_texture — when any backdrop draw exists this frame, the entire frame renders
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// here instead of the swapchain (Approach B). Copied to the swapchain
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// at frame end. Acts as the bracket's snapshot input by virtue of
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// already containing the pre-bracket frame.
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// here instead of the swapchain. Copied to the swapchain at frame
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// end. Acts as the bracket's snapshot input by virtue of already
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// containing the pre-bracket frame.
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// downsample_texture — written by the downsample PSO. Read by the blur PSO in mode 0.
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// h_blur_texture — written by the blur PSO in mode 0. Read by the blur PSO in mode 1.
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source_texture: ^sdl.GPUTexture,
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@@ -243,7 +244,7 @@ create_pipeline_2d_backdrop :: proc(
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//----- Downsample PSO ----------------------------------
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// Single bilinear sample, blend disabled. No vertex buffer (gl_VertexIndex 0..2 emits the
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// fullscreen triangle). Single-sample target (the ¼-res working textures are never MSAA).
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// fullscreen triangle). Single-sample target (working textures are never MSAA).
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downsample_target := sdl.GPUColorTargetDescription {
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format = swapchain_format,
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blend_state = sdl.GPUColorTargetBlendState{enable_blend = false},
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@@ -350,9 +351,9 @@ destroy_pipeline_2d_backdrop :: proc(device: ^sdl.GPUDevice, pipeline: ^Pipeline
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// ---------------------------------------------------------------------------------------------------------------------
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// Allocate (or reallocate, on resize) the three working textures that the backdrop bracket
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// uses. `source_texture` is full swapchain resolution; the other two are ¼-res. All single-
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// sample, all share the swapchain format, all need {.COLOR_TARGET, .SAMPLER} usage so they
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// can be written by render passes and read by subsequent passes.
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// uses. All three are sized at full swapchain resolution, single-sample, share the swapchain
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// format, and need {.COLOR_TARGET, .SAMPLER} usage so they can be written by render passes
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// and read by subsequent passes.
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//
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// Recreates on dimension change only — same-size frames hit the early-out and skip GPU
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// resource churn.
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@@ -466,19 +467,19 @@ ensure_backdrop_textures :: proc(device: ^sdl.GPUDevice, format: sdl.GPUTextureF
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// `i in [1, pair_count)` and does two texture fetches per pair — one at +offset, one at
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// -offset — for a total of 1 + 2*(pair_count-1) bilinear fetches per fragment.
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//
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// `sigma` is the true Gaussian standard deviation in the kernel's working-space units (¼-res
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// texels, after the caller has converted from logical pixels via dpi_scaling and the
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// downsample factor). The kernel extent reaches ±3σ, capturing 99.7% of the Gaussian's
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// `sigma` is the true Gaussian standard deviation in the kernel's working-space units
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// (working-resolution texels, after the caller has converted from logical pixels via
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// dpi_scaling and the downsample factor). The kernel extent reaches ±3σ, capturing 99.7% of
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// the Gaussian's
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// mass; weights beyond that contribute imperceptibly. sigma <= 0 produces a degenerate
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// kernel `{1, 0}` that acts as a sharp pass-through. After the loop, the discrete weights
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// are normalized so they sum to 1.0 (truncating at ±3σ loses a tiny amount of mass; we
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// renormalize to preserve overall image brightness).
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//
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// Earlier versions of this routine ported RAD Debugger's algorithm verbatim, which derives
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// stdev from a tap-count parameter (`stdev = (blur_count-1)/2`). That made the parameter
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// name misleading: the user thought they were passing σ but were actually passing
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// half-kernel-width. This version takes σ directly and derives the tap count from it,
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// matching what callers expect when they read "gaussian_sigma".
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// Note on the parameter contract: this routine takes σ directly and derives the tap count
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// from it, rather than the inverse (RAD Debugger's algorithm passes a tap count and derives
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// `stdev = (blur_count-1)/2`). Taking σ directly matches what callers expect when they read
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// "gaussian_sigma" — passing tap count under that name was a footgun.
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@(private)
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compute_blur_kernel :: proc(sigma: f32, kernel: ^[MAX_BACKDROP_KERNEL_PAIRS][4]f32) -> (pair_count: u32) {
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if sigma <= 0 {
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@@ -624,7 +625,7 @@ upload_backdrop_primitives :: proc(device: ^sdl.GPUDevice, pass: ^sdl.GPUCopyPas
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// ---------------------------------------------------------------------------------------------------------------------
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// Returns true if any sub-batch in any layer this frame is .Backdrop kind. Called once at the
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// top of `end()` to decide whether to route the whole frame to source_texture (Approach B).
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// top of `end()` to decide whether to route the whole frame to source_texture.
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// O(total sub-batches) but with an early-exit on the first hit, so typical cost is tiny.
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@(private)
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frame_has_backdrop :: proc() -> bool {
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@@ -742,10 +743,10 @@ compute_backdrop_group_work_region :: proc(
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// target viewport, per-primitive SDF discard handles masking and applies the tint. Each
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// sub-batch in the group is one instanced draw.
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//
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// V-blur was historically combined with the composite into a single shader invocation, but
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// that produced a horizontal-vs-vertical asymmetry artifact (horizontal source features
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// looked sharper than vertical ones inside the panel). Splitting V-blur into its own
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// working→working pass restores symmetry by making H and V blurs structurally identical.
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// V-blur is run as its own working→working pass rather than folded into the composite. The
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// folded variant produces a horizontal-vs-vertical asymmetry artifact (horizontal source
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// features end up looking sharper than vertical ones inside the panel). Matching V's
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// structure exactly to H's restores symmetry.
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//
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// On exit, source_texture contains the pre-bracket contents plus all backdrop primitives
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// composited on top. The caller then runs Pass B (post-bracket non-backdrop sub-batches) on
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@@ -1011,8 +1012,8 @@ run_backdrop_bracket :: proc(
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// geometry. The caller sets `color` (tint) on the returned primitive before submitting.
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//
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// No rotation, no outline — backdrop primitives are intentionally limited to axis-aligned
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// RRects in v1. Rotation breaks screen-space blur sampling visually; outline would be a
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// specialized edge effect that belongs in its own primitive type.
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// RRects. Rotation breaks screen-space blur sampling visually; outline would be a specialized
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// edge effect that belongs in its own primitive type.
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@(private)
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build_backdrop_primitive :: proc(
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rect: Rectangle,
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