Affine Effect Shader

PbmnLuv

A cheap try at reproducing the Affine Effect of older consoles for 3D games.

 

Shader code
shader_type spatial;

render_mode unshaded, cull_disabled, depth_prepass_alpha;

uniform float affineRadius = 4.0;
uniform float affineIntensity = 400;

uniform sampler2D image : source_color, repeat_enable;

uniform vec2 uv_scale = vec2(1.0,1.0);
varying float vertex_force;

void vertex() {
	vec3 vertex_world_pos = (MODEL_MATRIX*vec4(VERTEX,1.0f)).xyz;
	float true_dist = distance(CAMERA_POSITION_WORLD, vertex_world_pos);
	
	if (true_dist <= 0.001){
		vertex_force = 1.0/affineIntensity*length(UV)+1.0;
		
	}
	else {
		vertex_force = affineRadius/true_dist/affineIntensity*length(UV)+1.0;	
	}
	
}

void fragment() {
	vec2 new_uv = UV;
	if (uv_scale[0] > 0.0f || uv_scale[1] > 0.0f){
		
		new_uv[0] *= uv_scale[0];
		new_uv[1] *= uv_scale[1];
	
	}

	vec4 new_image;
	new_image = texture( image, new_uv*vertex_force);
	
	ALBEDO = new_image.rgb;
	ALPHA = new_image.a;
	
	
}
Tags
90s, affine, effect, ps1, psx, retro
The shader code and all code snippets in this post are under CC0 license and can be used freely without the author's permission. Images and videos, and assets depicted in those, do not fall under this license. For more info, see our License terms.

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laffcat
laffcat
28 days ago

nice work, but afaik this one-liner in vertex() – taken from a PSX shader by dsoft20 – gets the job done:

POSITION /= abs(POSITION.w);  // discard depth for affine mapping

(but ive only ever used it in gd3, for the record)

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PbmnLuv
PbmnLuv
28 days ago
Reply to  laffcat

Just tested that, I couldn’t make it work with just that line, everything turned invisible. It probably needs some other line to work? Maybe it’s a godot 4 thing, idk.

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laffcat
laffcat
28 days ago
Reply to  PbmnLuv

weird. the shader in question also has this line, i assumed it was for the position rounding in the shader but maybe it’s needed for the affine trick too:

VERTEX = VERTEX;  // it breaks without this - not sure why
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DmLPresents
DmLPresents
9 days ago
Reply to  PbmnLuv

You need to build the vertex position first:

//build the position default matrix
POSITION = PROJECTION_MATRIX * MODELVIEW_MATRIX * vec4(VERTEX, 1.0); 
// discard the perspective corrections
POSITION /= abs(POSITION.w);
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