Texture Masking

What it does

This shader maps a texture into other texture/sprite depending on position within the target texture, its size and the zoom pretended.

Params

hidden_texture – The texture to be revealed

position – position of our object within the given hidden_texture

zoom – basically how modified the size of the mask’s texture is (could be used to simulate a magnifying lense, for example). If you want a one per one representation of the hidden_texture make this param the scale/size of the corresponsing texture/sprite

size – how modified do we want the target hidden_texture to be. As a point of comparison, use the scale of a sprite with the hidden_texture assigned to it

Use Cases

– Revealing only part of an image (https://reallyokeyfruit.itch.io/bye-bye-birdy)

– Simulating Magnifying glass

How it works

It maps each UV coordinate of the main texture taking into account all parameters, using the following equation: (position.x + (UV.x - 0.5) * zoom * float(textureSize(TEXTURE, 0).x))) / (float(textureSize(hidden_texture, 0).x) * size) + 0.5;

Then it changes that UV coordinate’s color, if the alpha in that specific coordinate is bigger then 0, to the corresponding color in the hidden_texture

Godot Version: 4.1

Shader code

shader_type canvas_item;

uniform sampler2D hidden_texture;
uniform vec2 position = vec2(0, 0);
uniform float zoom = 1.0;
uniform float size = 10.0;

void fragment() {
	vec4 main_color = texture(TEXTURE, UV);
	float UV_target_x = 
		(position.x + 
		((UV.x - 0.5) * zoom * float(textureSize(TEXTURE, 0).x)))
		/ (float(textureSize(hidden_texture, 0).x) * size)
		+ 0.5;
		 
	float UV_target_y = 
		(position.y + 
		((UV.y - 0.5) * zoom * float(textureSize(TEXTURE, 0).y)))
		/ (float(textureSize(hidden_texture, 0).y) * size)
		+ 0.5;
		
	if (main_color.a != 0.0) {
		COLOR.rgba = texture(hidden_texture, vec2(UV_target_x, UV_target_y)).rgba;
	} 
}

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