wip: engine enhancements and fixes

assets/shaders/gl_textured.vert

@@ -0,0 +1,23 @@
+#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);
+}