Shaderpack Bugs

This file tracks some bugs in shader packs that might appear to be Iris issues, but are just bugs within the shader pack.

All shader packs

Vanilla shadows appear in addition to dynamic shadows
- Diagnosis: Shader packs force there to be shadows where there is low skylight to prevent light from leaking into caves. While I would like to make this workaround unnecessary, it is entirely something implemented in the shaderpack, Iris doesn't really have control over it.
- Workaround: no general workaround, each pack implements this differently.

Enchantment glints don't render
- Diagnosis: This is because the TAA jitter is applied to entities, but not to enchantment glints. The enchantment glint must be transformed in the exact same way as the entity it is being applied to or else it will break.
- Workaround: Replace TemporalJitterProjPos(gl_Position); with // TemporalJitterProjPos(gl_Position); on line 116 of gbuffers_entities.vsh
- Confirmation: This bug has been confirmed to be observable in both Iris and OptiFine.

Enchantment glints have z-fighting in the nether and end
- Diagnosis: In the nether and end, gbuffers_armor_glint uses a series of matrix multiplications, but gbuffers_textured uses ftransform. The matrix multiplications introduce precision errors compared to ftransform that cause the vertex depths to be subtly different, which is enough to cause issues with the glint effect. The glint must have the exact same transformations as the content it's being applied to in order to work properly, otherwise issues like this show up.
- Fix: Replace the content of lines 27-29 of gbuffers_armor_glint.vsh with gl_Position = ftransform();
- Tracking issue: Sildurs-shaders/sildurs-shaders.github.io#158
Block breaking animations have weird colors at certain camera angles, and don't show up on chests / other block entities.
- Diagnosis: No gbuffers_damagedblock program is provided, meaning that gbuffers_terrain is used for rendering block breaking animations. This program is not set up to handle translucency, causing the weird colorations due to it blending oddly with existing terrain data. Furthermore, since the deferred rendering code handles terrain separately from block entities, the block breaking animation is written to the terrain render target instead of being blended with the block entity.
- Workaround: unknown.

Random flashing holes in the terrain
- Diagnosis: Some waving parameters are left uninitialized instead of being initialized to zero, causing some non-waving blocks to get undefined vertex positions. This appears to be caused by a failed attempt to initialize all parameters to zero using only a single assignment.
- Workaround: Apply the following diff:
```
-	float parm0,parm1,parm2,parm3,parm4,parm5 = 0.0;
+	float parm0 = 0.0,parm1 = 0.0,parm2 = 0.0,parm3 = 0.0,parm4 = 0.0,parm5 = 0.0;
```
Shadows don't work
- Diagnosis: Table 3.20 in section 3.9.2 of the OpenGL 3.3 Core Profile specification states clearly that when the base internal format of a texture is RED / DEPTH_COMPONENT, which is true in the case of a shadow texture, then the Y/G and Z/B components of the output of a sampler function are 0.0. However, Chocapic v4 accesses the Z/B component to get the depth value. While this may have worked on older drivers, it no longer appears to work on modern drivers.
- Workaround: Replace all occurrences of expressions along the lines of texture2D(shadow, ...).z with texture2D(shadow, ...).r