implement sky rendering

src/main/resources/assets/crystalline_sky/shaders/core/terrain_sky.fsh

@@ -0,0 +1,22 @@
+#version 150
+
+#moj_import <minecraft:fog.glsl>
+#moj_import <minecraft:dynamictransforms.glsl>
+
+uniform sampler2D Sampler0;
+
+in float sphericalVertexDistance;
+in float cylindricalVertexDistance;
+in vec4 texProj0;
+
+out vec4 fragColor;
+
+void main() {
+    vec4 color = textureProj(Sampler0, texProj0) * ColorModulator;
+#ifdef ALPHA_CUTOUT
+    if (color.a < ALPHA_CUTOUT) {
+        discard;
+    }
+#endif
+    fragColor = apply_fog(color, sphericalVertexDistance, cylindricalVertexDistance, FogEnvironmentalStart, FogEnvironmentalEnd, FogRenderDistanceStart, FogRenderDistanceEnd, FogColor);
+}

src/main/resources/assets/crystalline_sky/shaders/core/terrain_sky.vsh

@@ -0,0 +1,26 @@
+#version 150
+
+#moj_import <minecraft:fog.glsl>
+#moj_import <minecraft:dynamictransforms.glsl>
+#moj_import <minecraft:projection.glsl>
+
+in vec3 Position;
+in vec4 Color;
+in vec2 UV0;
+in ivec2 UV2;
+in vec3 Normal;
+
+uniform sampler2D Sampler2;
+
+out float sphericalVertexDistance;
+out float cylindricalVertexDistance;
+out vec4 texProj0;
+
+void main() {
+    vec3 pos = Position + ModelOffset;
+    gl_Position = ProjMat * ModelViewMat * vec4(pos, 1.0);
+
+    sphericalVertexDistance = fog_spherical_distance(pos);
+    cylindricalVertexDistance = fog_cylindrical_distance(pos);
+    texProj0 = projection_from_position(gl_Position);
+}