Why does my Godot ColorRect shader render flat color?

The shader must be shader_type canvas_item. If it is spatial or particles, the shader compiles but does not apply to ColorRect. Also confirm a ShaderMaterial (not Shader) is assigned to the material slot.

How do I write a fullscreen post-process shader in Godot for ColorRect?

Use shader_type canvas_item. Sample SCREEN_TEXTURE for the framebuffer beneath. Place a ColorRect covering the viewport with the ShaderMaterial assigned. Set the rect's mouse filter to Ignore so it does not block input.

Why does use_parent_material change the rendering?

With use_parent_material true, the ColorRect uses its parent's material instead of its own. Useful for batching effects across multiple children but disables independent control of this rect's shader.

Fix: Godot ColorRect Shader Not Applying

Quick answer: Use shader_type canvas_item for ColorRect shaders. Assign a ShaderMaterial resource (with the shader inside) to the rect’s Material slot, not a raw Shader.

Here is how to fix Godot 4 ColorRect that ignores its shader and renders as flat color. The shader type and material wrapper must match what canvas_item rendering expects.

The Symptom

You write a shader, drop it on the ColorRect material slot. The rect renders as plain color, ignoring the shader entirely.

What Causes This

Wrong shader_type. Spatial or particles shaders compile but cannot apply to canvas_item nodes.

Shader vs ShaderMaterial confusion. The Material slot wants a Material resource (ShaderMaterial), not the bare Shader resource.

use_parent_material on. Hides the rect’s own material in favor of the parent’s.

The Fix

Step 1: Use canvas_item shader type.

shader_type canvas_item;

void fragment() {
    COLOR.rgb = vec3(sin(TIME), UV.x, UV.y);
}

Step 2: Wrap in ShaderMaterial. In Project view, right-click → New Resource → ShaderMaterial. Open it; drag your .gdshader into the Shader slot. Drag the ShaderMaterial into the ColorRect’s Material slot.

Step 3: For full-screen post-process.

shader_type canvas_item;

uniform sampler2D screen_tex : hint_screen_texture, repeat_disable, filter_nearest;

void fragment() {
    vec4 col = texture(screen_tex, SCREEN_UV);
    col.rgb = 1.0 - col.rgb;   // invert
    COLOR = col;
}

Add a ColorRect filling the viewport with this material. Set Mouse Filter to Ignore so it does not capture clicks.

Step 4: Confirm use_parent_material is off. ColorRect inspector → Material → Use Parent Material = false (unless intentionally sharing).

Step 5: Test in editor preview. Edit the rect’s color or shader uniforms; preview should update live. If not, the shader is not actually applied.

“canvas_item type. ShaderMaterial wrapper. use_parent_material off. ColorRect renders the shader.”

Related Issues

For shader uniform texture binding, see Shader Texture Hints. For shader color banding, see Shader Banding.

canvas_item, ShaderMaterial, no parent inherit. Pixel shader applies.