GM Shaders Mini: Environments
How to use HDRI textures in GM
Hi people!
Today let's talk about environment mapping! It's actually surprisingly simple to set up. Let's explore how to use it.
Tutorial Difficulty: Intermediate
What Is An Environment Map?
An environment map is a panorama texture that gives a complete 360-degree view of the surrounding environment. GameMaker doesn't support cubemaps for environments, but that's okay. We can use equirectangular or HDRI textures as a common alternative:
Fun fact: This is the same projection used on most world maps (only external instead of internal)!
These can be used to texture skyboxes, for reflections and much more.
Texture Coordinates
In order to use these we need to convert a vec3 direction vector to vec2 texture coordinates. It's important to understand how these textures are formatted. The texture's x-coordinate represents the horizontal direction (yaw) from 0 to 360 degrees. And the y-coordinate represents the pitch from -90 to 90 degrees. For trig fans, this is just the spherical polar coordinates!
We can calculate this yaw-direction like so:
float yaw = atan(direction.y, direction.x);Note: atan(y,x) is short for arctangent, or in other words, it computes the direction of our vector (in radians). It's very similar to point_direction(0,0,x,y) or arctan2(y,x) in GML. If you want to learn more, I wrote about it in detail here!
Now we can compute the pitch direction:
float pitch = asin(clamp(direction.z, -1.0, 1.0));So asin(x) is just the inverse of sine. It takes the ratio of the opposite side and the hypotenuse and returns the angle (in radians).
Now to use these coordinates we need to map them to the 0-1 range. Since we're using radians, atan ranges from -pi to +pi and asin from -pi/2 to pi/2. Just some simple math to normalize them:
#define PI 3.1415926
vec2 sphere_uv = vec2(yaw/PI*0.5+0.5, pitch/PI+0.5);You can use these UV coordinates to sample your texture!
Skybox and Reflections!
For starters, this can be used to texture your skybox in a shader. Just compute the direction from the camera to the skybox like so:
vec3 direction = normalize(v_world_pos.xyz - u_camera);Here we're using the world-space coordinate from the vertex shader:
v_world_pos = gm_Matrices[MATRIX_WORLD] * vec4(in_Position, 1.0);Note: The world space parts are optional. They're just for when you rotate, scale or translate a model using the world matrix!
And u_camera which should be a uniform 3D camera's position.
This direction can then be converted to texture coordinates and used to sample the sky texture!
If you want to do reflective objects, copy the skybox shader, but add this:
vec3 ref_direction = reflect(direction, v_world_normal);This uses our view direction to reflect off of world-space normals.
I compute my world-space normals like this (vertex shader):
v_world_normal= normalize((gm_Matrices[MATRIX_WORLD] * vec4(in_Normal, 0.0)).xyz);Let's test it on a sphere! Looks beautiful
You can also try refracting or sampling for directional lighting using environment textures! I'll leave those experiments up to you to try.
I've put together a little example on ShaderToy with all the code we've covered so far!
How to Find Them
So you may be wondering how you can get a texture like these? Well my favorite place is PolyHaven HDRI. PolyHaven has tons of high-quality textures that are free to use even in commercial projects (licensed under CC0). They include HDR data, which GM doesn't currently support, but you can convert them to PNGs using a photo editor like GIMP.
Or you can search Google for "environment maps", "reflection maps" or "HDRI". Just make sure you have permission to use them if you plan on releasing anything with them!
Conclusion
By now you have a new tool at your disposal! I've used this just recently in jam game called Haven:
There are a lot of effects going on here, but one of the greatest additions was the subtle reflections on the blocks. I hope you can find some cool uses for this technique in your own games (maybe even in 2D?).
Anyway, Happy Thanksgiving to all who celebrate it, and thanks for reading.
Have a great night!