66 lines
1.8 KiB
GLSL
66 lines
1.8 KiB
GLSL
|
#version 330 core
|
||
|
|
|
||
|
|
in vec2 texcoord;
|
||
|
|
in vec4 cloud_color;
|
||
|
|
in vec4 ap_color;
|
||
|
|
|
||
|
|
uniform sampler2D base_tex;
|
||
|
|
|
||
|
|
uniform mat4 osg_ProjectionMatrix;
|
||
|
|
uniform vec4 fg_Viewport;
|
||
|
|
uniform vec3 fg_SunDirection;
|
||
|
|
|
||
|
|
uniform float density = 30.0;
|
||
|
|
uniform float max_sample_dist = 0.05;
|
||
|
|
|
||
|
|
const int STEPS = 8;
|
||
|
|
|
||
|
|
// aerial_perspective.glsl
|
||
|
|
vec3 mix_aerial_perspective(vec3 color, vec4 ap);
|
||
|
|
|
||
|
|
vec4 cloud_common_frag()
|
||
|
|
{
|
||
|
|
vec4 base = texture(base_tex, texcoord);
|
||
|
|
|
||
|
|
// Directly discard fragments below a threshold
|
||
|
|
if (base.a < 0.02)
|
||
|
|
discard;
|
||
|
|
|
||
|
|
// Pixel position in screen space [-1, 1]
|
||
|
|
vec2 screen_uv = ((gl_FragCoord.xy - fg_Viewport.xy) / fg_Viewport.zw) * 2.0 - 1.0;
|
||
|
|
|
||
|
|
// XXX: Sun's screen-space position. This should be passed as an uniform
|
||
|
|
vec4 sun_dir_screen = osg_ProjectionMatrix * vec4(fg_SunDirection, 0.0);
|
||
|
|
sun_dir_screen.xyz /= sun_dir_screen.w;
|
||
|
|
sun_dir_screen.xyz = normalize(sun_dir_screen.xyz);
|
||
|
|
|
||
|
|
// Direction from pixel to Sun in screen space
|
||
|
|
vec2 sun_dir = screen_uv - sun_dir_screen.xy;
|
||
|
|
// Flip the x axis
|
||
|
|
sun_dir.x = -sun_dir.x;
|
||
|
|
|
||
|
|
float dt = max_sample_dist / STEPS;
|
||
|
|
|
||
|
|
// 2D ray march along the Sun's direction to estimate the transmittance
|
||
|
|
float T = 1.0;
|
||
|
|
for (int i = 0; i < STEPS; ++i) {
|
||
|
|
float t = (float(i) + 0.5) * dt;
|
||
|
|
vec2 uv_t = texcoord - sun_dir * t;
|
||
|
|
vec4 texel = texture(base_tex, uv_t);
|
||
|
|
// Beer-Lambert's law
|
||
|
|
T *= exp(-texel.a * dt * density);
|
||
|
|
}
|
||
|
|
|
||
|
|
// When the camera is facing perpendicularly to the Sun, the Sun's
|
||
|
|
// screen-space location can tend toward infinity. Fade the effect toward
|
||
|
|
// the perpendicular.
|
||
|
|
float fade = smoothstep(0.1, 0.5, dot(vec3(0.0, 0.0, -1.0), fg_SunDirection));
|
||
|
|
|
||
|
|
vec4 color = base * cloud_color;
|
||
|
|
color.rgb *= base.a * mix(0.5, T, fade);
|
||
|
|
|
||
|
|
color.rgb = mix_aerial_perspective(color.rgb, ap_color);
|
||
|
|
|
||
|
|
return color;
|
||
|
|
}
|