Optimizing GLSL Shaders for Real-Time Performance

Shaders are essential for creating visual effects in TouchDesigner, games, and real-time graphics. However, inefficient shaders can slow down performance. This article will cover simple ways to make GLSL shaders faster and smoother.

1. Reduce Expensive Calculations

Some math functions are slow. Instead of using pow(), sin(), or exp(), try using simpler alternatives.

✅ Faster code:

float brightness = value * value; 

The second version avoids the expensive pow() function and works almost the same.

2. Minimize Texture Lookups

Every time you use texture(), the GPU reads from memory, which can slow things down.

🚫 Inefficient texture sampling:

vec4 tex1 = texture(sampler1, uv);
vec4 tex2 = texture(sampler2, uv);
vec4 finalColor = mix(tex1, tex2, 0.5);

✅ Faster approach:

vec4 tex = texture(samplerAtlas, uv); // Use a single texture atlas

Using fewer texture lookups reduces GPU workload.

3. Avoid if-else Statements

Conditional logic (if, else) can slow down fragment shaders. Instead, use built-in GLSL functions like mix() or step().

🚫 Slow branching:

if (value > 0.5) {
    color = vec3(1.0, 0.0, 0.0); // Red
} else {
    color = vec3(0.0, 0.0, 1.0); // Blue
}

✅ Optimized version:

color = mix(vec3(0.0, 0.0, 1.0), vec3(1.0, 0.0, 0.0), step(0.5, value));

This removes the if statement, making the shader run faster.

4. Use Lower-Precision Where Possible

If high precision isn’t needed, use mediump instead of highp. This saves GPU resources, especially on mobile devices.

✅ Example:

mediump float value = texture(sampler, uv).r;

5. Optimize Performance in TouchDesigner

When using GLSL TOP in TouchDesigner:

• Use TOP nodes to handle some effects instead of coding everything in GLSL.
• Reduce the number of feedback loops to avoid unnecessary GPU work.
• Use 1D Look-Up Tables (LUTs) for color effects instead of complex math.