glsl — consolidated language guide — DedSec Project

GLSL

Typical use: Graphics shader languages.

Suggested file extension: .glsl.

How to run / environment: Compile as a fragment shader in a supported graphics host.

Starter example

#version 330 core
out vec4 FragColor;
void main() { FragColor = vec4(0.2, 0.5, 0.8, 1.0); }

How to read it

Shaders compute pixels, so no console print is available.

Common pitfall

Shaders compute pixels, so no console print is available.

GLSL — Expanded practice workbook

Read the baseline source

#version 330 core
out vec4 FragColor;
void main() { FragColor = vec4(0.2, 0.5, 0.8, 1.0); }

Relevant environment: Compile as a fragment shader in a supported graphics host.. Verify that the matching compiler, host or simulator is available before treating output as authoritative. For scripts that can interact with personal files or systems, use a scratch workspace and read-only fixtures by default.

Detailed working objective

Implement a fragment color gradient from normalized UV coordinates and clamp the output. Compare linear color values with sRGB display and test coordinate extremes.

The failure that must be understood

GLSL versions and OpenGL ES precision qualifiers differ; a shader that compiles on desktop may fail on mobile GPUs.

GLSL — Focused mastery pathway

Objective and environment

Create one desktop OpenGL 3.3 fragment shader that draws a soft-edged circle on a UV gradient. This is GLSL 330 core, not a drop-in OpenGL ES shader: ES needs its own version declaration and platform-appropriate precision handling. The host must supply interpolated UV coordinates named v_uv and link a matching vertex stage.

Fragment shader (circle.frag)

#version 330 core
in vec2 v_uv;
out vec4 fragColor;
uniform float u_radius;

void main() {
    vec2 uv = clamp(v_uv, vec2(0.0), vec2(1.0));
    float distanceFromCenter = length(uv - vec2(0.5));
    float circle = 1.0 - smoothstep(
        u_radius - 0.01, u_radius + 0.01, distanceFromCenter
    );
    vec3 background = vec3(uv.x, uv.y, 0.2);
    fragColor = vec4(mix(background, vec3(1.0, 0.9, 0.2), circle), 1.0);
}

The fragment input is an interpolated varying, not a pixel position. The shader clamps UV deliberately: outside-range UVs collapse to an edge color instead of repeating. The smoothstep transition is 0.02 UV units wide; the apparent width in pixels varies with the rendered surface. This shader does not perform sRGB conversion; that belongs to the selected render target and host configuration.

Test matrix and diagnostics

1. Set u_radius=0.25. At UV (0.5,0.5) the circle blend should be 1; at (0,0) it should be 0; at (1,1) it should be 0.
2. At UV (0.75,0.5) the boundary midpoint should blend near 0.5 because the distance equals the radius.
3. Render a non-square viewport and check whether the circle looks elliptical. If so, account for aspect ratio in the distance calculation.
4. Deliberately change v_uv to a mismatched vertex output name: inspect the link diagnostic, not only the fragment compilation.
5. Check an OpenGL ES build separately. Copying #version 330 core into an ES-only context is an environment mismatch, not an algorithm bug.

Completion evidence

Keep the complete vertex/fragment pair, exact OpenGL context version, compile and link logs, screenshots for the four UV cases, and any host-side color-space settings. Without an actual GL host, this is a static shader exercise, not a confirmed GPU rendering test.

GLSL — Technical notes and common pitfalls

Core knowledge

1. Shader stages have different input and output contracts and execution constraints.
2. Coordinate spaces and precision choices affect numerical correctness.
3. Test inside a matching graphics pipeline rather than treating shaders as ordinary command-line scripts.