glsl.md

glsl

This API consists of an extremely simple structure of OpenGL objects and a small set of functions that operate upon it.

• glsl.c
• glsl.h

The structure contains a program object, vertex and fragment shader objects, and character pointers used to cache shader file names, if provided.

struct glsl
{
    GLuint program;

    GLuint vert_shader;
    GLuint frag_shader;

    char  *vert_filename;
    char  *frag_filename;
};

typedef struct glsl glsl;

The functions that initialize and release these resources are as follows.

• GLboolean glsl_source(glsl *G, const char *vert_str, int vert_len, const char *frag_str, int frag_len);

  Initialize a GLSL program object using the given vertex shader source string vert_str and fragment shader source string frag_str. If these strings are not null-terminated then vert_len and frag_len give their lengths. If they are null-terminated, these lengths may be given as -1. In the event of an error in shader compilation or program linking, the relevant log contents are printed to the standard error stream and GL_FALSE is returned.

• GLboolean glsl_create(glsl *G, const char *vert_filename, const char *frag_filename);

  Initialize a GLSL program object using the named vertex shader source file vert_filename and fragment shader source file frag_filename. These file names are cached within the GLSL structure. On error, relevant log contents are printed to the standard error stream and GL_FALSE is returned.

• void glsl_delete(glsl *G);

  Release the shader objects, program object, and cached file names held by the given GLSL structure.

Once initialized, the program entry of the glsl structure may be used normally.

glsl G;

if (glsl_create(&G, "phong.vert", "phong.frag"))
    glUseProgram(G.program);

A few convenience functions are also provided.

• GLint glsl_uniform(GLuint, const char *, ...);

  Return the location of a GLSL uniform. This is a more powerful form of the glGetUniformLocation function taking a variable arguments list that enables the construction of array and structure uniform names in the style of printf. For example, to initialize an array of sampler uniforms in a loop:

    for (int i = 0; i < 16; i++)
        glUniform1i(glsl_uniform(G.program, "image[%d]", i), i);
  

• GLboolean glsl_reload(glsl *G);

  If the given GLSL structure was initialized using glsl_create and the shader file names are cached then glsl_reload flushes and reloadss the current shader and program objects. This allows modified shader files to be activated without stopping and restarting the running application.