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130 lines
7 KiB
Markdown
130 lines
7 KiB
Markdown
This info pertains to the Blurs by TroggleMonkey:
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DESCRIPTION:
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Gaussian blurs are common building blocks in multi-pass shaders, and this
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library of optimized and tested blurs should make it easier to use whatever size
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blur you need. All of these shaders are based on the tex2Dblur* functions in
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include/blur-functions.h, so you can use those directly if you ever need to
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add more processing to the same pass as a Gaussian blur.
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PICK THE RIGHT BLUR FOR YOUR USE CASE:
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There are several different types of blurs, ranging in size from 3-12 texels:
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a.) "Resize" separable blurs use vertical and horizontal passes and require N
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taps for an Nx blur. These are arbitrarily resizable.
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b.) "Fast" separable blurs use vertical and horizontal passes and require N taps
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for an (N*2 - 1)x blur. They exploit bilinear filtering to reduce the
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required taps from e.g. 9 to 5. These are always faster, but they have
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strict image scale requirements.
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c.) "Resize" one-pass blurs combine the vertical/horizontal passes of the
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"resize" separable blurs, and they require NxN taps for an NxN blur. These
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perform slowly enough that only tex2Dblur3x3resize is useful/included.
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d.) Other one-pass blurs combine the vertical/horizontal passes of the "fast"
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separable blurs, and they exploit bilinear filtering the same way. They're
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faster than separable blurs at 3x3, competitive at 5x5 depending on options,
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and slower at 7x7 and above...but larger blurs may still be useful if you're
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hurting for passes.
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e.) "Shared" one-pass blurs go a step further: They also use quad-pixel
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communication with fine-grained derivatives to distribute texture samples
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across a 2x2 pixel quad. (ddx() and ddy() are required, as well as a GPU
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that uses fine-grained derivatives). These blurs are faster than the other
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one-pass blurs, but they have some artifacts from combining sample-sharing
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with bilinear sampling, so they're best reserved for reblurring an already-
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blurred input.
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Every blur expects linear filtering. Except for resize separable blurs, all
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require a pass scale of (1/(2^M)) for some M >= 0. That is, the output image
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has to have a 1:1 pixel:texel ratio with some mipmap of the input image, so use
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e.g. scaleN = "1.0" or scaleN = "0.25", not scaleN = "0.33" or scaleN = "2.0".
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Note: mipmap_inputN must = "true" in your .slangp file for scales other than 1.0.
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There are two suffixes on the .slang files relating to gamma correction:
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* Blurs with no suffix assume linear RGB input and output.
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* Blurs with a "-last-pass" suffix use pow() to gamma-correct their output.
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* Blurs with a "-gamma-encode-every-fbo" suffix use pow() to linearize each
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input sample and again to gamma-correct the output. These blurs are MUCH
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slower than blurs without this suffix, but they're provided in case you want
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to be [almost] gamma-correct on platforms without sRGB FBO's. (The "almost"
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is because bilinear filtering still won't be gamma-correct without sRGB.)
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* There are also blurs with both suffixes. This may seem redundant, but they
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make it easier to use a different output gamma for the last pass than for
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the rest of the pipeline (such as when simulating another display device like
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a Game Boy Advance or CRT). See srgb-helpers/README.txt for more information.
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BENCHMARK RESULTS:
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Blurs have different performance characteristics depending on whether the input
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is mipmapped and depending on whether they're gamma-encoding every FBO. Here's
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an excerpt from the blur-functions.h description with a comparison. Note that
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benchmarks without an sRGB heading use "-gamma-encode-every-fbo" suffixes, and
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you can just look at the sRGB performance figures if you don't care about gamma:
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// Here are some framerates from a GeForce 8800GTS. The first pass resizes to
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// viewport size (4x in this test) and linearizes for sRGB codepaths, and the
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// remaining passes perform 6 full blurs. Mipmapped tests are performed at the
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// same scale, so they just measure the cost of mipmapping each FBO (only every
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// other FBO is mipmapped for separable blurs, to mimic realistic usage).
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// Mipmap Neither sRGB+Mipmap sRGB Function
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// 76.0 92.3 131.3 193.7 tex2Dblur3fast
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// 63.2 74.4 122.4 175.5 tex2Dblur3resize
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// 93.7 121.2 159.3 263.2 tex2Dblur3x3
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// 59.7 68.7 115.4 162.1 tex2Dblur3x3resize
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// 63.2 74.4 122.4 175.5 tex2Dblur5fast
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// 49.3 54.8 100.0 132.7 tex2Dblur5resize
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// 59.7 68.7 115.4 162.1 tex2Dblur5x5
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// 64.9 77.2 99.1 137.2 tex2Dblur6x6shared
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// 55.8 63.7 110.4 151.8 tex2Dblur7fast
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// 39.8 43.9 83.9 105.8 tex2Dblur7resize
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// 40.0 44.2 83.2 104.9 tex2Dblur7x7
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// 56.4 65.5 71.9 87.9 tex2Dblur8x8shared
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// 49.3 55.1 99.9 132.5 tex2Dblur9fast
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// 33.3 36.2 72.4 88.0 tex2Dblur9resize
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// 27.8 29.7 61.3 72.2 tex2Dblur9x9
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// 37.2 41.1 52.6 60.2 tex2Dblur10x10shared
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// 44.4 49.5 91.3 117.8 tex2Dblur11fast
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// 28.8 30.8 63.6 75.4 tex2Dblur11resize
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// 33.6 36.5 40.9 45.5 tex2Dblur12x12shared
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BASIC USAGE:
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The .slangp presets in the quality-test-presets folder provide usage examples
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for basically every .slang blur shader. The "-srgb" suffix on some .slangp
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presets is an explicit notice that they use sRGB FBO's. Note how and when the
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"-last-pass" suffix is used for each .slang file, etc.
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The provided .slangp files with the "-mipmap" suffix are used to test quality and
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benchmarking with mipmapping enabled, but none of them actually use mipmapping
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as a feature in and of itself. The following contrived .slangp would do that:
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shaders = "4"
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# Pass0: Linearize RGB:
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shader0 = ../../srgb-helpers/first-pass-linearize.slang
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filter_linear0 = "true"
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scale_type0 = "source"
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scale0 = "1.0"
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srgb_framebuffer0 = "true"
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# Pass1: Upsize to 4x. Pretend this pass does significant processing at 4x.
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shader1 = ../../stock.slang
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filter_linear1 = "true"
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scale_type1 = "source"
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scale1 = "4.0"
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srgb_framebuffer1 = "true"
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# Pass2: Blur a source-sized mipmap 9x vertically; just shrink horizontally.
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shader2 = ../blur9fast-vertical.slang
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filter_linear2 = "true"
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scale_type2 = "source"
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scale2 = "0.25"
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srgb_framebuffer2 = "true"
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mipmap_input = "true"
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# Pass3: Blur 9x horizontally
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shader3 = ../blur9fast-horizontal.slang
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filter_linear3 = "true"
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scale_type3 = "source"
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scale3 = "1.0"
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srgb_framebuffer3 = "true"
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# Pass4: Scale to the screen size and gamma-correct the output:
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shader4 = ../../srgb-helpers/last-pass-gamma-correct.slang
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filter_linear4 = "true"
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scale_type4 = "viewport"
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scale4 = "1.0"
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