# Terrain effect
# This effect uses prodecural shader splatting, you most likely want to modify
# it with your own texture-map generation code.

vertex:
    inout: |
        uniform struct {
            sampler2D data_texture;
            sampler2D heightfield;
            int view_index;
            int terrain_size;
            int chunk_size;
        } ShaderTerrainMesh;
        out vec2 terrain_uv;

    transform: |
        // Terrain data has the layout:
        // x: x-pos, y: y-pos, z: size, w: clod
        vec4 terrain_data = texelFetch(ShaderTerrainMesh.data_texture,
        ivec2(gl_InstanceID, ShaderTerrainMesh.view_index), 0);

        // Get initial chunk position in the (0, 0, 0), (1, 1, 0) range
        vec3 chunk_position = p3d_Vertex.xyz;

        // CLOD implementation
        float clod_factor = smoothstep(0, 1, terrain_data.w);
        chunk_position.xy -= clod_factor * fract(chunk_position.xy * ShaderTerrainMesh.chunk_size / 2.0)
                              * 2.0 / ShaderTerrainMesh.chunk_size;

        // Scale the chunk
        chunk_position *= terrain_data.z * float(ShaderTerrainMesh.chunk_size)
                        / float(ShaderTerrainMesh.terrain_size);
        chunk_position.z *= ShaderTerrainMesh.chunk_size;

        // Offset the chunk, it is important that this happens after the scale
        chunk_position.xy += terrain_data.xy / float(ShaderTerrainMesh.terrain_size);

        // Compute the terrain UV coordinates
        terrain_uv = chunk_position.xy;

        // Sample the heightfield and offset the terrain - we do not need to multiply
        // the height with anything since the terrain transform is included in the
        // model view projection matrix.
        chunk_position.z += texture(ShaderTerrainMesh.heightfield, terrain_uv).x;

        // Lower the terrain on the borders - this ensures the shadow map is generated
        // correctly.
        if ( min(terrain_uv.x, terrain_uv.y) < 8.0 / ShaderTerrainMesh.terrain_size ||
           max(terrain_uv.x, terrain_uv.y) > 1 - 9.0 / ShaderTerrainMesh.terrain_size) {
           chunk_position.z = 0;
        }

        vOutput.position = (p3d_ModelMatrix * vec4(chunk_position, 1)).xyz;

fragment:
    defines: |
        #define DONT_FETCH_DEFAULT_TEXTURES 1
        #define DONT_SET_MATERIAL_PROPERTIES 1

    inout: |
        layout(location=4) in vec2 terrain_uv;
        layout(location=5) uniform struct {
            sampler2D data_texture;
            sampler2D heightfield;
            int view_index;
            int terrain_size;
            int chunk_size;
        } ShaderTerrainMesh;

    material: |

        // Compute terrain normal
        const float terrain_height = 1000.0;
        vec3 pixel_size = vec3(1.0, -1.0, 0) / textureSize(ShaderTerrainMesh.heightfield, 0).xxx;
        float h_u0 = texture(ShaderTerrainMesh.heightfield, terrain_uv + pixel_size.yz).x * terrain_height;
        float h_u1 = texture(ShaderTerrainMesh.heightfield, terrain_uv + pixel_size.xz).x * terrain_height;
        float h_v0 = texture(ShaderTerrainMesh.heightfield, terrain_uv + pixel_size.zy).x * terrain_height;
        float h_v1 = texture(ShaderTerrainMesh.heightfield, terrain_uv + pixel_size.zx).x * terrain_height;
        vec3 tangent = normalize(vec3(1, 0, h_u1 - h_u0));
        vec3 binormal = normalize(vec3(0, 1, h_v1 - h_v0));
        vec3 normal = normalize(cross(tangent, binormal));

        normal.x *= -1;
        // normal.y *= -1;

        // Material splatting
        float height = (h_u0 + h_u1 + h_v0 + h_v1) / (4.0 * terrain_height); // xxx
        float slope = 1.0 - normal.z;
        float grass = 0.0;
        float rock = 0.0;
        float snow = 0.0;

        { // Snow
            snow = saturate(4.0 * (height-0.49));
            snow *= saturate(pow(saturate(1.0 - slope), 2.0)) * 12.0;

            //snow -= 0.6;
            //snow *= 0.5;
            snow = saturate(snow);
            snow = pow(snow, 2.0);
        }

        { // Rock
            rock = saturate((pow(slope, 1.2) * 12.0 - 0.02) * 4.5);
        }

        { // Grass
            grass = 1.0 - saturate(rock + snow);
        }


        // Material definitions

        MaterialShaderOutput grass_mat = make_default_material_output();
        grass_mat.basecolor = vec3(0.1, 0.2, 0.1);
        grass_mat.roughness = 0.8;

        MaterialShaderOutput rock_mat = make_default_material_output();
        rock_mat.basecolor = vec3(0.13);
        rock_mat.roughness = 0.8;
        rock_mat.specular_ior = 1.4;

        MaterialShaderOutput snow_mat = make_default_material_output();
        snow_mat.basecolor = vec3(0.6, 0.6, 0.9);
        snow_mat.roughness = 0.5;
        snow_mat.specular_ior = 1.7;

        m.basecolor = vec3(0);
        m.shading_model = SHADING_MODEL_DEFAULT;
        m.specular_ior = 0.0;
        m.metallic = 0.0;
        m.roughness = 0.0;
        m.shading_model_param0 = 0.0;
        m.normal = vec3(0);

        merge_material_output(m, grass_mat, grass);
        merge_material_output(m, rock_mat, rock);
        merge_material_output(m, snow_mat, snow);

        m.normal = normal;