Yoshi's Island Shimmer - Heat Haze Distortion

This is a simple yet powerful post-processing shader adapted for Godot’s CanvasItem that applies a subtle, persistent distortion or wobble to the entire screen. This effect is ideal for simulating heat haze, liquid surfaces, magical aura, or the “shimmering” effect often used for visual feedback (like a character getting a power-up or, as noted, a “Yoshi dancing” effect).

The core effect is achieved by:

Noise Flow: The UV coordinates for the noise_texture are animated over time, creating continuous, seamless motion.
Distortion Map: The red (x) and green (y) channels of the sampled noise are used to create a $2 D$ offset vector.
Screen Warp: This offset vector is scaled by the strength uniform and added to the SCREEN_UV, causing the final image to subtly warp and distort based on the flowing noise pattern.

Adjustable Uniforms (Shader Parameters):

Parameter	Type	Description
noise_texture	`sampler2D`	Required Input: A seamless noise texture (e.g., Perlin, Simplex) used as the source for the distortion map.
strength	`float`	Controls the intensity of the distortion (how much the screen warps). Keep this value very low (e.g., `< 0.01`).
speed	`vec2`	Controls the speed and direction of the noise pattern’s movement over time.
SCREEN_TEXTURE	`sampler2D`	Required Input: Provides the image of the scene to be distorted.

Shader code

shader_type canvas_item;

uniform sampler2D noise_texture : source_color, repeat_enable;
uniform float strength : hint_range(0.0, 0.05, 0.001) = 0.005;
uniform vec2 speed = vec2(0.1, 0.05);
uniform sampler2D SCREEN_TEXTURE : hint_screen_texture, filter_linear_mipmap;


void fragment() {
    vec2 noise_uv = UV + TIME * speed;

    vec2 offset = (texture(noise_texture, noise_uv).xy * 2.0 - 1.0);

    offset *= strength;
 vec2 distorted_uv = SCREEN_UV + offset;
    
    COLOR = texture(SCREEN_TEXTURE, distorted_uv);
}