Fix backdrop-filter: blur generating excessive mipmap levels (#10340)#10370
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Fix backdrop-filter: blur generating excessive mipmap levels (#10340)#10370Infiland wants to merge 1 commit intoFacepunch:masterfrom
Infiland wants to merge 1 commit intoFacepunch:masterfrom
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…ch#10340) The backdrop blur shader samples at MIP level sqrt(BlurScale / 2), which is typically 2-5 for normal blur values, but GrabFrameTexture was always generating the full mipmap chain (~11 levels). Each level requires a Gaussian blur compute shader dispatch and GPU barrier. Now only the mip levels the shader will actually sample are generated. When no blur is applied (e.g. backdrop-filter: brightness only), mipmap generation is skipped entirely.
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Summary
Backdrop-filter blur panels were generating the full mipmap chain (~11 levels) regardless of the actual blur amount needed. The shader only samples at MIP level
sqrt(BlurScale / 2)(typically 2-5 for normal values), so most compute dispatches were wasted. This change limits mipmap generation to only the levels the shader will actually sample, and skips it entirely when no blur is applied (e.g.backdrop-filter: brightnessonly).Motivation & Context
Since version 26.04.01, panels with
backdrop-filter: blurcause significant FPS drops around 50%. Each backdrop panel triggers a full framebuffer copy + Gaussian blur compute shader dispatch and GPU barrier for every mip level. With ~11 levels generated but only 2-5 neededFixes: #10340
Implementation Details
maxMipsparameter (default 0 = all mips for backward compatibility). When maxMips > 0, the render target is created with fewer mip levels, so GenerateMipMaps naturally processes fewer levels.ceil(sqrt(blurScale / 2)) + 2(+2 for trilinear filtering safety margin). Rounds up to even for render target pool stability. UsesDownsampleMethod.Nonewhen blur is 0.Existing callers (Bloom, SSR, Highlight, BasePostProcess) are unaffected by the default maxMips = 0.
Screenshots / Videos (if applicable)
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