Custom Sprite Batcher in LibGDX

This is an advanced tutorial that will deal with shaders, meshes, camera matrices, texture handling, and various other concepts. Ensure you have read and understand the following before continuing:

• Handling Textures in LibGDX
• Shader Tutorial Series
• Intro to Sprite Batchers

Objective

As we know from previous tutorials, we can send float data to a shader with uniforms (vec2, vec3, etc). The problem is, however, that we need to flush the SpriteBatch before changing the uniform. Imagine each of our sprites require a different uniform value; this would lead to a lot of flushing, and it defeats the benefits of a SpriteBatch in the first place.

The solution is to use vertex attributes -- this allows us to send data to the shader per-vertex as opposed to per-batch. We already use vertex attributes to send RGBA colors per sprite, or texture coordinates per vertex. There are a number of situations where custom vertex data will prove useful, but for our cases let's use it for multi-texturing.

Theoretical Puzzle Game

Let's say we're developing a simple puzzle game. One option would be to pre-render all the masked pieces offline, in Photoshop or with a custom tool. Another option is to apply the masking in real-time, on the GPU. For the latter, we can use the same techniques discussed in Shader Lesson 4 to mask our puzzle photo.