4.1 KiB
Python+GLSL Shader Deblocking Sample
This sample demonstrates how to use a simple pixel shader to greatly reduce ASTC texture block artifacts, which can be quite noticeable when the block size goes beyond roughly 6x6. The basic idea: instead of always sampling the texture using a single tap, you instead sample the texture either one time or X times with a simple low pass filter, depending on whether or not the sample location is near a block edge. The multiple filter taps around the center sample blur across block boundaries of ASTC compressed textures.
The example shader is compatible with mipmapping, bilinear filtering, trilinear filtering etc. The shader smoothly lerps between no filtering and edge filtering, and is mipmap-aware by using the pixel shader derivative instructions. The Python sample shows either a textured quad or a cube, with various controls to move the object, rotate the cube, toggle the deblocking shader on/off, trilinear off/on, etc.
It was written to be as simple as possible. It's also possible to add adaptivity to this shader, so it doesn't blindly blur across sharp edges - like we do while CPU deblocking before transcoding to BC7 or other LDR texture formats. It's also possible to add deblocking filter awareness to our ASTC/XUASTC/etc. encoders.
Note: We're amazed the GPU hardware vendors haven't implemented this feature directly in silicon yet. It's obviously extremely useful.
You'll need these Python dependencies to run it:
pip install numpy Pillow glfw PyOpenGL
You may also want "PyOpenGL_accelerate", and under Linux you may need to also install the system package "libglfw3". We developed this sample under Windows 11.
See run.bat for the command line on how to run the sample. Or run:
py -3.12 testbed.py shader.glsl 12 12 flower_unpacked_rgb_ASTC_LDR_12X12_RGBA_level_0_face_0_layer_0000.png flower_unpacked_rgb_ASTC_LDR_12X12_RGBA_level_1_face_0_layer_0000.png flower_unpacked_rgb_ASTC_LDR_12X12_RGBA_level_2_face_0_layer_0000.png flower_unpacked_rgb_ASTC_LDR_12X12_RGBA_level_3_face_0_layer_0000.png flower_unpacked_rgb_ASTC_LDR_12X12_RGBA_level_4_face_0_layer_0000.png
Depending on your setup you may need to use 'python' or 'python3' etc.
The shader can be easily simplified to sample the texture less by using less taps. The current shader uses a total of 9 taps, but 5 are possible.
Many variations and optimizations of this basic idea are possible.
Screenshots - ASTC 12x12 Block Size
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Enabled:
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Usage and Controls
The sample either renders a single textured quad or a cube. Press 'C' to toggle between the quad and the cube. The '1' key toggles shader deblocking (off by default). The '2' key enables edge visualization, which only works when deblocking is enabled.
Other keys can be used to move around the quad, rotate the cube etc.:
Usage:
python testbed.py shader.glsl block_w block_h mip0.png mip1.png [mip2.png ...]
block_w, block_h: Block size in texels (e.g. 8 8 for 8x8 DCT blocks)
Controls:
Arrows Move quad left/right/up/down
W / S Move closer / farther
A / D Rotate yaw (cube mode)
Q / E Rotate pitch (cube mode)
C Toggle cube / quad mode
B Bilinear filtering
T Trilinear filtering
P Point filtering
R Reload shader
1 Toggle deblocking shader off/on
2 Toggle edge visualization (only when deblocking active)
3-4 Toggle shader const0.x/y/z/w (0 <-> 1)
5-8 Toggle shader const1.x/y/z/w (0 <-> 1)
Space Reset to initial state
Esc Quit
Credits
The included sunflower image is in the CC0/Public Domain, and was downloaded from here:
https://www.publicdomainpictures.net/en/view-image.php?image=756601&picture=large-yellow-sunflower
"License: CC0 Public Domain - Lynn Greyling has released this “Large Yellow Sunflower” image under Public Domain license."