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Backdrop Fragment Shader
#version 150
// Const
const float PI = 3.14159265358979323846;
// Uniforms
uniform sampler2D tex; // Skysphere texture
uniform mat4 v; // View matrix
uniform vec3 pos; // Camera position
uniform vec4 gridColor; // Grid color
// Input
in Block
{
noperspective vec3 viewRay;
}
ib;
// Output
out vec4 color;
// Grid distance to XZ-plane positioned at [0, 0, 0]
float gridDistance(vec3 origin, vec3 dir)
{
return length(dir * origin.y / dir.y);
}
// Grid color
// Adjust constants to your liking (line width, etc.)
vec4 grid(vec2 p, vec4 color)
{
float frq = PI / 8.0;
return color * smoothstep(.98, 1.2,
max(1.05 * sin((p.x + 4.0) * frq), 1.05 * sin((p.y + 4.0) * frq)));
}
// Sphere color
vec4 sphere(vec3 p, sampler2D tex)
{
vec2 uv = vec2(0.5 - atan(p.z, p.x) / (2 * PI), 0.5 - asin(p.y) / PI);
return texture(tex, uv);
}
void main(void)
{
// Ray pointing into the scene
vec3 ray = normalize(ib.viewRay) * mat3(v);
// Grid distance (intersection distance to plane)
float gd = gridDistance(pos, ray);
// Final color (sphere color + grid color with distance falloff)
color = sphere(ray, tex) +
max(0, 1 - gd * 0.0015) * grid((pos + gd * ray).xz, gridColor);
}
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