Add essentials

resources/shaders/gl_textured.frag

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+#version 330 core
+
+in  vec3 v_normal;
+in  vec2 v_tex;
+in  vec3 v_position;
+
+out vec4 frag_color;
+
+uniform vec3 u_light;
+uniform sampler2D tex;
+uniform vec3 color; // base colour factor (acts as solid colour when no texture)
+
+void main() {
+    // Combine base texture (or constant white) with colour factor supplied by CPU.
+    vec3 base_col = texture(tex, v_tex).rgb * color;
+
+    vec3 ambient_color  = base_col * 0.2;
+    vec3 diffuse_color  = base_col * 0.6;
+    vec3 specular_color = vec3(1.0);
+
+    // u_light is the direction **from the light towards the fragment**.
+    float diffuse = max(dot(normalize(v_normal), normalize(u_light)), 0.0);
+
+    vec3 camera_dir = normalize(-v_position);
+    vec3 half_dir   = normalize(normalize(u_light) + camera_dir);
+    float specular  = pow(max(dot(half_dir, normalize(v_normal)), 0.0), 16.0);
+
+    vec3 result = ambient_color + diffuse * diffuse_color + specular * specular_color;
+
+    // Convert from linear to sRGB for display (approximate γ-correction)
+    result = pow(result, vec3(1.0 / 2.2));
+
+    frag_color = vec4(result, 1.0);
+}

resources/shaders/gl_textured.vert

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+#version 330 core
+
+in vec3 position;
+in vec3 normal;
+in vec2 tex_coords;
+
+uniform mat4 model;
+uniform mat4 view;
+uniform mat4 projection;
+uniform vec2 uv_offset;
+uniform vec2 uv_scale;
+
+out vec3 v_normal;
+out vec2 v_tex;
+out vec3 v_position;
+
+void main() {
+    mat4 modelview = view * model;
+    v_normal   = transpose(inverse(mat3(modelview))) * normal;
+    v_tex      = tex_coords * uv_scale + uv_offset;
+    v_position = (modelview * vec4(position, 1.0)).xyz;
+    gl_Position = projection * modelview * vec4(position, 1.0);
+}

resources/shaders/skybox.frag

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+#version 330 core
+
+in vec3 direction;
+
+out vec4 frag_color;
+
+uniform sampler2D equirect;
+
+const vec2 inv_atan = vec2(0.15915494309, 0.31830988618);
+
+vec2 sample_spherical_map(vec3 v) {
+    vec2 uv = vec2(atan(v.z, v.x), asin(v.y));
+    uv *= inv_atan;
+    uv += 0.5;
+    return uv;
+}
+
+void main() {
+    vec2 uv = sample_spherical_map(normalize(direction));
+    vec3 color = texture(equirect, uv).rgb;
+    frag_color = vec4(color, 1.0);
+} 

resources/shaders/skybox.vert

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+#version 330 core
+
+in vec3 position;
+
+uniform mat4 view;
+
+uniform mat4 projection;
+
+out vec3 direction;
+
+void main() {
+    direction = position;
+    vec4 pos = projection * view * vec4(position, 1.0);
+    gl_Position = pos.xyww;
+}