Input ports may be declared as abstract GLSL functions

[xian]

Example transition shader below. Note that the functions channelA and channelB below have no body, so they become input ports. If arguments are passed to them, those values will be injected (by content type) into any shaders routed through that port. That is, the value supplied for uv will override any injected uv-coordinate value requested by shaders via that input port.

// @param uv uv-coordinate
// @return color
vec4 channelA(vec2 uv);

// @param uv uv-coordinate
// @return color
vec4 channelB(vec2 uv);

uniform float fade; // @type float

// @return color
vec4 main() {
    if (1. - gl_FragCoord.x > fade) {
        return channelA(gl_FragCoord + vec2(fade, 0));
    } else {
        return channelB(gl_FragCoord + vec2(fade - 1., 0));
    }
}

Screen.Recording.2021-03-12.at.5.19.16.PM.mov

See also related subject matter:

• ISF's Transitions spec
• GL Transition Specification v1