r3d/shaders/generic/screen.vert

/* screen.vert -- Generic vertex shader for rendering a full-screen quad
 *
 * Copyright (c) 2025-2026 Le Juez Victor
 *
 * This software is provided 'as-is', without any express or implied warranty.
 * For conditions of distribution and use, see accompanying LICENSE file.
 */

#version 330 core

const vec2 positions[3] = vec2[]
(
    vec2(-1.0, -1.0),
    vec2( 3.0, -1.0),
    vec2(-1.0,  3.0)
);

noperspective out vec2 vTexCoord;

void main()
{
    // Here Z is fixed at 1.0.
    // For fullscreen passes that match the depth buffer resolution:
    //   - GL_EQUAL allows rendering only the background
    //   - GL_GREATER allows invoking the shader only on geometry

    gl_Position = vec4(positions[gl_VertexID], 1.0, 1.0);
    vTexCoord = (gl_Position.xy * 0.5) + 0.5;
}