Difference between revisions of "3D Fundamentals Tutorial 10"
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You can see a video that really exaggerates what affine (warpy) textures look like [https://youtu.be/8IRT3SdRz8c?t=1260 here]. | You can see a video that really exaggerates what affine (warpy) textures look like [https://youtu.be/8IRT3SdRz8c?t=1260 here]. | ||
| + | |||
| + | <div class="mw-collapsible mw-collapsed"><br /> | ||
| + | * The need for perspective correction: texture warping [https://youtu.be/1Dv2-cLAJXw?t=0m47s 0:47] | ||
| + | * Explanation & visualization of the problem [https://youtu.be/1Dv2-cLAJXw?t=1m57s 1:57] | ||
| + | <div class="mw-collapsible-content"> | ||
| + | :* Linear mapping of screen coordinates to texture coordinates is not correct | ||
| + | :* Reason: interpolation in screenspace is different from interpolation in object space (and all attributes of the object) | ||
| + | :* We need "foreshortening": far things get compressed, close things get expanded | ||
| + | </div> | ||
| + | * The math: the z divide makes mapping nonlinear [https://youtu.be/1Dv2-cLAJXw?t=4m28s 4:28] | ||
| + | * Solution: interpolate between the z-divided texture coordinates [https://youtu.be/1Dv2-cLAJXw?t=5m00s 5:00] | ||
| + | * Implementing this into code [https://youtu.be/1Dv2-cLAJXw?t=8m40s 8:40] | ||
| + | <div class="mw-collapsible-content"> | ||
| + | :* In <code>PubeScreenTransformer.h</code> (where the projection / z-divide is applied) | ||
| + | :* In <code>Pipeline.h</code> (where the interpolation is done) [https://youtu.be/1Dv2-cLAJXw?t=10m57s 10:57] | ||
| + | </div> | ||
| + | * Demo [https://youtu.be/1Dv2-cLAJXw?t=11m57s 11:57] | ||
| + | * How perspective correction was (not) handled in early 3d games [https://youtu.be/1Dv2-cLAJXw?t=12m16s 12:16] | ||
| + | <div class="mw-collapsible-content"> | ||
| + | :* To fully correct, you need an expensive reciprocal operation 1/z for every pixel drawn | ||
| + | :* Some awful examples of badly handled perspective drawing [https://youtu.be/1Dv2-cLAJXw?t=13m45s 13:45] | ||
| + | </div> | ||
| + | * Solution used in hardware pipelines / GPUs [https://youtu.be/1Dv2-cLAJXw?t=14m11s 14:11] | ||
| + | <div class="mw-collapsible-content"> | ||
| + | :* Control how each vertex attribute is interpolated independently (interpolation modifiers) | ||
| + | </div> | ||
| + | * References to full math derivations [https://youtu.be/1Dv2-cLAJXw?t=14m50s 14:50] | ||
| + | * Side effect of our solution: we now have the correct z-values for each pixel [https://youtu.be/1Dv2-cLAJXw?t=16m20s 16:20] | ||
| + | </div> | ||
== Downloads == | == Downloads == | ||
Revision as of 02:37, 10 June 2020
In this tutorial we get the butt wiggling texture to respect our authoritae! In other words, we upgrade our affine texture mapping to perspective-correct texture mapping, putting the kibosh on the fucked-up texture distortion.
Video
The tutorial video is on YouTube here.
You can see a video that really exaggerates what affine (warpy) textures look like here.
- The need for perspective correction: texture warping 0:47
- Explanation & visualization of the problem 1:57
- Linear mapping of screen coordinates to texture coordinates is not correct
- Reason: interpolation in screenspace is different from interpolation in object space (and all attributes of the object)
- We need "foreshortening": far things get compressed, close things get expanded
- The math: the z divide makes mapping nonlinear 4:28
- Solution: interpolate between the z-divided texture coordinates 5:00
- Implementing this into code 8:40
- In
PubeScreenTransformer.h(where the projection / z-divide is applied) - In
Pipeline.h(where the interpolation is done) 10:57
- In
- To fully correct, you need an expensive reciprocal operation 1/z for every pixel drawn
- Some awful examples of badly handled perspective drawing 13:45
- Solution used in hardware pipelines / GPUs 14:11
- Control how each vertex attribute is interpolated independently (interpolation modifiers)
Downloads
The GitHub repository for the tutorial code is here.
