投影 Projection

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shader_type canvas_item;

uniform vec2  offset = vec2(2.0,2.0);
uniform vec4  shadow:source_color = vec4(0,0,0,0.5);

void fragment(){
    vec2 px = TEXTURE_PIXEL_SIZE*offset;
    vec4 s = vec4(shadow.rgb, shadow.a*texture(TEXTURE, UV+px).a);
    vec4 b = texture(TEXTURE, UV);
    COLOR = max(s, b);
}