It’s a mix.
Under the hood a matchbox shader is glsl code (to be executed directly on the GPU). Most community matchboxes have been left in readable/open source form and you can see what they do and modify them.
There is a choice to ‘compile’ them into a single .mx file, which is more like a .zip file. It can optionally be encrypted which would obscure the contents.
Lastly there is the special case of nodes that are referred to as Matchbox, but that are in fact custom code. All those are ADSK made, and an example is Image.
Regarding crok_pixelspread, that is in fact a readable shader. If you install the logik matchbox shaders via the portal, you should find the file in /opt/Autodesk/presets/“flame version”/shaders/matchbox/LOGIK/…
Here’s the main code file:
vec3 adsk_getDiffuseMapCoord();
vec4 adsk_getDiffuseMapValue(in vec2 texCoord);
uniform float adskUID_amount;
float adskUID_alpha(vec2 uv)
{
return adsk_getDiffuseMapValue(uv.xy).a;
}
vec4 adskUID_lightbox(vec4 source)
{
vec3 uv = adsk_getDiffuseMapCoord();
vec2 size_inv=vec2(1.0 / 2000.0, 1.0 / 2000.0);
float p_amount = -1.0 * adskUID_amount;
float cr=cos(0.0);
float sr=sin(0.0);
mat3 g_trans = mat3( cr*p_amount*size_inv.x, sr*p_amount*size_inv.y, 0.0, -sr*p_amount*size_inv.x, cr*p_amount*size_inv.y, 0.0, 0.0, 0.0, 1.0 );
vec4 disp_h = vec4(adskUID_alpha(uv.xy+vec2(0.0,size_inv.y)),adskUID_alpha(uv.xy+vec2(0.0,-size_inv.y)),adskUID_alpha(uv.xy+vec2(-size_inv.x,0.0)),adskUID_alpha(uv.xy+vec2(size_inv.x,0.0)));
vec4 disp_d = vec4(adskUID_alpha(uv.xy+size_inv),adskUID_alpha(uv.xy-size_inv),adskUID_alpha(uv.xy+vec2(-size_inv.x,size_inv.y)),adskUID_alpha(uv.xy+vec2(size_inv.x,-size_inv.y)));
disp_h = max( disp_h, 0.0);
disp_d = max( disp_d, 0.0);
vec4 levels = vec4(1.0);
disp_h = pow( disp_h, levels );
disp_d = pow(disp_d, levels );
vec2 gradient = vec2(0.0);
gradient.x = dot( disp_h, vec4(0.0, 0.0, 2.0, -2.0)) + dot( disp_d, vec4(-1.0, 1.0, 1.0, -1.0));
gradient.y = dot( disp_h, vec4(-2.0, 2.0, 0.0, 0.0)) + dot( disp_d, vec4(-1.0, 1.0, -1.0, 1.0));
gradient = ( g_trans * vec3( gradient, 1.0)).xy;
vec4 col = vec4(adsk_getDiffuseMapValue(uv.xy+gradient ).rgb, 1.0);
return vec4(col.rgb, source.a);
}
