add(/wiki/virtual-sprites): draft from 7th May 2025

Author: Longor1996

content/wiki/virtual-sprites/index.md

@@ -0,0 +1,86 @@
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+title = "Virtual Sprites"
+description = "Dynamically building an atlas of used sprites at runtime."
+draft = true
+[taxonomies]
+categories = ["rendering"]
+tags = ["rendering", "texturing"]
++++
+
+> Dynamically building an atlas and index of sprites at runtime...
+
+{{ todo_notice(body="This article is incomplete and explains an experimental technique.") }}
+
+## Motivation
+
+{{ todo_notice(body="Convert to paragraphs? Explain better?") }}
+
+- Building a texture atlas at start-up of *all* the sprites is quite the expensive process.
+- Array textures are limited to ~2048 layers and require all sprites to have the same size.
+- Both a normal atlas and array-textures have trouble with animated textures.
+- Uploading small textures/sprites to the GPU is surprisingly fast and easy.
+- As chunk meshes depend on their used sprites, we can't save/restore them to disk.
+- Being able to dynamically create new sprites at runtime as needed is neat.
+- Being able to let sprites have special projections and parameters is neat.
+- Surprisingly this is doable, though slower, with older OpenGL versions!
+  - (iirc, older GPUs/drivers don't like random-ish memory/texture reads?)
+
+Silly things one can do with this technique:
+
+- 'Environmental' sprites.
+- User-generated sprites.
+- Font glyphs and emoji.
+
+Drawbacks:
+
+- Whomst cares?
+
+## Implementation
+
+{{ todo_notice(body="Finish (minimal) implementation?") }}
+
+```glsl
+#version 460 core
+
+struct SpriteDef {
+	float uv[4];
+};
+
+layout(binding = 0, std430) readonly buffer ssbo_sprites {
+	SpriteDef sprites[];
+};
+
+struct Facelet {
+	int data0; // position, dimensions, rotation
+	int data1; // colortint, corner-ao, ...
+	int data2; // spriteref, spritearg, ...
+}
+
+layout(binding = 1, std430) readonly buffer ssbo_faces {
+	Facelet facelets[];
+};
+
+struct Meshlet {
+	mat4 transform;
+	int facelets_start;
+	int facelets_count;
+}
+
+layout(binding = 2, std430) readonly buffer ssbo_meshlets {
+	Meshlet meshlets[];
+};
+```
+
+---
+
+{{ todo_notice(body="Recommended: Face Pulling") }}
+{{ todo_notice(body="Requirement: SSBOs or BufferTextures") }}
+
+## See also
+
+- [Face Pulling](/wiki/face-pulling)
+- [Vertex Pooling](/wiki/vertex-pooling)
+
+## References
+
+- [SSBOs](https://ktstephano.github.io/rendering/opengl/ssbos)