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wgpu backend: lighting parity, MSAA, cavity shading, fix sRGB output

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Closes the visible gap to BonsaiViewer down to just the post-process
edge silhouette pass (still pending in task #9). Four changes bundled
because together they bring up the parity story:

  - WGSL fragment now applies cavity = clamp(length(fwidth(n))*1.5,
    0, 0.35) and multiplies by (1 - cavity). Matches GL shader.

  - Lighting constants switched to GL's exact values: key (0.3, 0.5,
    0.8), fill (-0.3, -0.5, 0.8), sky tint (0.55, 0.60, 0.70), ground
    tint (0.35, 0.32, 0.28). My initial guesses were close but not
    identical; matching them means side-by-side diffs only flag actual
    pipeline differences, not lighting tweaks.

  - 4× MSAA: render pass writes into a MULTISAMPLE color attachment
    (surface_format_-matched), resolves into the surface texture for
    present. Depth is also 4 samples. Pipeline.multisample.count = 4.
    ensureMsaaColorTexture / releaseMsaaColorTexture mirror the depth-
    texture lifecycle. Matches GL minimal's QSurfaceFormat::setSamples(4).

  - sRGB output fix. wgpu-native's Vulkan swap chain on X11 treats
    BGRA8Unorm as sRGB-output (applies linear→sRGB encoding on shader
    writes), even though caps.formats[0] reports plain Unorm. The GL
    backend writes to a non-sRGB framebuffer with no such conversion,
    so a clearValue of (0.125, 0.137, 0.161) lands as bytes (32, 35,
    41) on GL but (99, 104, 112) on wgpu — ~3× brighter. Pre-decoding
    via srgbToLinear on (a) the clearValue in C++ and (b) the final
    fragment colour in WGSL makes wgpu's implicit encode round-trip,
    so the final bytes match GL. Verified via screenshot pixel sample:
    #202329 background reads as exactly (32, 35, 41).

Remaining visible gap to BonsaiViewer is the dark-line edge silhouettes
(renderEdgePass in GL, depth laplacian → outline). That belongs with
the overlay / post-process work in task #9.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
This commit is contained in:
Dion Moult
2026-05-27 14:44:13 +10:00
parent a95437dd64
commit 4596f2e584
2 changed files with 91 additions and 16 deletions
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src/ifcviewer-wgpu/WgpuViewportWindow.h
+11 -1
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@@ -109,6 +109,8 @@ private:
void buildModelBindGroup(WgpuModelGpuData& m);
void ensureDepthTexture(int w, int h);
void releaseDepthTexture();
void ensureMsaaColorTexture(int w, int h);
void releaseMsaaColorTexture();
void updateFrameUniforms();
void flushPendingSidecarQueue();
bool computeSceneAabb(float mn[3], float mx[3]) const;
@@ -142,12 +144,20 @@ private:
WGPUBuffer frame_uniform_buffer_ = nullptr;
WGPUBindGroup frame_bind_group_ = nullptr;
// Depth attachment, recreated on surface resize.
// Depth attachment (4× MSAA), recreated on surface resize.
WGPUTexture depth_texture_ = nullptr;
WGPUTextureView depth_view_ = nullptr;
int depth_w_ = 0;
int depth_h_ = 0;
// 4× MSAA color target. Surface format-matched, recreated on resize.
// The render pass writes here, then resolves into the surface texture.
WGPUTexture msaa_color_texture_ = nullptr;
WGPUTextureView msaa_color_view_ = nullptr;
int msaa_w_ = 0;
int msaa_h_ = 0;
static constexpr uint32_t SAMPLE_COUNT = 4;
QColor background_color_ = QColor("#202329");
// Camera (orbit, right-handed Y-up world → wait, BIM is +Z up).