There are many cases where you need to compute a simple projection or model-view matrix, but you don't need a full linear algebra library. glt was built for exactly this case. It emulates the OpenGL 1.0 transformation functions, but work on float arrays, that can then be passed to GLSL shaders.
glt provides the following functions:
void gltLoadIdentity(float* matrix);
void gltMultMatrix(float* matrix, float* other);
void gltOrtho(float* matrix, float left, float right, float bottom, float top, float near, float far);
void gltOrtho2D(float* matrix, float left, float right, float bottom, float top);
void gltFrustum(float* matrix, float left, float right, float bottom, float top, float near, float far);
void gltPerspective(float* matrix, float fovy, float aspect, float near, float far);
void gltLookAt(float* matrix, float eyex, float eyey, float eyez, float centerx, float centery, float centerz, float upx, float upy, float upz);
void gltTranslate(float* matrix, float x, float y, float z);
void gltRotate(float* matrix, float angle, float x, float y, float z);
void gltScale(float* matrix, float x, float y, float z);
And they work similar to their gl and glu counterparts. (Except that translate, rotate and scale do not have variants, only "3f".)
Using the library is quite simple and straight forward. For example if you want to compute a perspective projection matrix:
float projectionMatrix[16];
// width and height from window / screen size
float aspect = (float)width / (float)height;
gltPerspective(projectionMatrix, 45.0f, aspect, 0.1f, 1000.0f);
And a view matrix with LookAt works as well:
float modelViewMatrix[16];
glLoadIdentity(modelViewMatrix);
glLookAt(modelViewMatrix, -10.0f, 0.0f, 0.0f, 0.0f, 0.0f, 0.0f, 0.0f, 0.0f, 1.0f);
If you want to push and pop, you need to implement that yourself, but to add a model matrix to the view:
glTranslate(modelViewMatrix, 0.0f, 5.0f, 2.0f);
glRotate(modelViewMatrix, 30.0f, 0.0f, 0.0f);
Now you only need to pass that array to a uniform variable in your shader.
Copyright (c) 2015 Sean Farrell
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