shader-programming Checked

// Per-pixel: read the texture at this UV, multiply by a color (tint), keep alpha.
uniform sampler2D tex;
uniform vec4 tint;          // e.g. (1,0,0,1) reddens; multiply is non-destructive
in vec2 uv;                 // interpolated 0..1 texture coordinate (a "varying")
out vec4 frag;
void main() {
    vec4 c = texture(tex, uv);   // HLSL: tex.Sample(samp, uv)
    frag = c * tint;             // component-wise multiply tints without clipping
}

### 2. Scrolling UVs (animated texture) — frame-rate independent

// Add time * speed to the UV to scroll. fract() wraps it into 0..1 so it tiles.
uniform sampler2D tex;
uniform float time;          // seconds, supplied by the engine
uniform vec2 scroll_speed;   // UV units per second, e.g. (0.1, 0.0)
in vec2 uv;
out vec4 frag;
void main() {
    vec2 scrolled = fract(uv + scroll_speed * time);  // HLSL: frac(...)
    frag = texture(tex, scrolled);
}
// Drive with a real time uniform, not a per-frame accumulator, so speed is stable.

### 3. Dissolve (threshold a noise map, glow the edge)

// Hide pixels where noise < threshold; tint a thin band at the boundary.
uniform sampler2D tex;
uniform sampler2D noise_tex;     // grayscale noise, 0..1
uniform float amount;            // 0 = fully visible, 1 = fully dissolved
uniform float edge = 0.05;       // width of the glowing edge band
uniform vec4 edge_color;
in vec2 uv;
out vec4 frag;
void main() {
    vec4 c = texture(tex, uv);
    float n = texture(noise_tex, uv).r;
    if (n < amount) discard;                 // cut away dissolved pixels
    float e = smoothstep(amount, amount + edge, n);  // 0 at the edge -> 1 inside
    frag = mix(edge_color, c, e);            // HLSL: lerp(edge_color, c, e)
}

### 4. Fresnel rim light (3D) — brighten glancing angles

// Rim = 1 where the surface faces away from the camera (silhouette glow).
in vec3 world_normal;        // normalized, world space (from the vertex stage)
in vec3 view_dir;            // normalized, surface -> camera, world space
uniform float power = 3.0;
uniform vec3 rim_color;
out vec4 frag;
void main() {
    float f = pow(1.0 - clamp(dot(world_normal, view_dir), 0.0, 1.0), power);
    frag = vec4(rim_color * f, 1.0);   // add to lighting; f peaks at the silhouette
}
// Correctness: normal and view_dir MUST be in the same space and normalized.

Pitfalls

• **Mixing coordinate spaces** (lighting a world-space normal against a

view-space light) yields subtly wrong shading. Pick one space and convert

everything into it.

• **Forgetting to normalize** interpolated normals/directions: interpolation

shortens vectors, so dot() results drift. normalize() in the fragment stage.

• **UV assumptions across engines.** Some engines flip V (top-left vs bottom-left

origin); a texture may appear upside-down. Know your engine's convention.

• **Heavy branching / dynamic loops** stall GPUs. Prefer step/smoothstep/

mix; reserve if/discard for genuinely cheap early-outs.

• **discard defeats early-Z** and can hurt performance on tiled mobile GPUs;

prefer alpha blending where you can.

• **Precision on mobile**: highp vs mediump matters; large UVs or time values

in low precision shimmer. Use adequate precision for coordinates and time.

• **Assuming GLSL == HLSL.** mix↔lerp, fract↔frac, texture()↔.Sample(),

vec2↔float2, column- vs row-major matrices. See the reference mapping.

References

• references/effects.md — full outline (2D sprite + 3D), vignette, and color

grading shaders; the GLSL↔HLSL function/type mapping table; per-engine notes

(Godot canvas_item/spatial, Unity ShaderLab/HLSL, Unreal material nodes).

Related skills

• godot-shaders — Godot shading language syntax, built-ins, and screen-reading.
• unreal-niagara — GPU particle VFX (a different shader use).
• procedural-gen — the noise that drives dissolve and procedural texturing.