mobiground/opengl.c

#include <stdlib.h>

#include <GL/glew.h>
#include <SDL3/SDL.h>
#include <SDL3/SDL_opengl.h>

#include "opengl.h"
#include "readfile.h"

shaderProgram_t sp;

GLuint createShader ( const char *shaderFile, GLenum shaderType )
{
    const char *strShaderType;
    if (shaderType == GL_VERTEX_SHADER) {
        strShaderType = "vertex";
    } else if (shaderType == GL_GEOMETRY_SHADER) {
        strShaderType = "geometry";
    } else if (shaderType == GL_FRAGMENT_SHADER) {
        strShaderType = "fragment";
    } else {
        SDL_LogCritical(SDL_LOG_CATEGORY_ASSERT, "Unrecognized shader type.");
        exit(EXIT_FAILURE);
    }
    GLuint shader = glCreateShader(shaderType);
    if (!shader) {
        SDL_LogCritical(SDL_LOG_CATEGORY_ASSERT, "Error create shader type %s.", strShaderType);
        exit(EXIT_FAILURE);
    }
    GLchar *content = readFile(shaderFile);
    glShaderSource(shader, 1, (const GLchar **)&content, NULL);
    SDL_free(content);
    glCompileShader(shader);
    GLint status;
    glGetShaderiv(shader, GL_COMPILE_STATUS, &status);
    if (status == GL_FALSE) {
        GLint infoLen;
        glGetShaderiv(shader, GL_INFO_LOG_LENGTH, &infoLen);
        GLchar *info = SDL_malloc(sizeof(GLchar) * (infoLen + 1));
        glGetShaderInfoLog(shader, infoLen, NULL, info);
        SDL_LogCritical(SDL_LOG_CATEGORY_ASSERT, "Filed to compile %s shader:\n%s.", strShaderType, info);
        exit(EXIT_FAILURE);
    }
    return shader;
}

void createProgram ( GLuint *shaders, int len )
{
    sp.program = glCreateProgram();
    if (!sp.program) {
        SDL_LogCritical(SDL_LOG_CATEGORY_ASSERT, "Can't to create shader program.");
        exit(EXIT_FAILURE);
    }
    for (int i = 0; i < len; i++) {
        glAttachShader(sp.program, shaders[i]);
    }
    glLinkProgram(sp.program);
    GLint status;
    glGetProgramiv(sp.program, GL_LINK_STATUS, &status);
    if (status == GL_FALSE) {
        GLint infoLen;
        glGetProgramiv(sp.program, GL_INFO_LOG_LENGTH, &infoLen);
        GLchar *info = SDL_malloc(sizeof(GLchar) * (infoLen + 1));
        glGetProgramInfoLog(sp.program, infoLen, NULL, info);
        SDL_LogCritical(SDL_LOG_CATEGORY_ASSERT, "Link failed: %s", info);
        exit(EXIT_FAILURE);
    }
}

void createBuffer ( void )
{
    GLushort indices[] = {
        0, 1, 2,
        0, 2, 3
    };
    float vertices[] = {
      -1.0f, -1.0f, -2.0f, 1.0f, // left-bottom
      -1.0f,  1.0f, -2.0f, 1.0f, // left-top
       1.0f,  1.0f, -2.0f, 1.0f, // right-top
       1.0f, -1.0f, -2.0f, 1.0f, // right-bottom

       // colours
       1.0f, 0.0f, 0.0f, 1.0f, // red
       0.0f, 1.0f, 0.0f, 1.0f, // green
       1.0f, 0.0f, 1.0f, 1.0f, // purple
       1.0f, 1.0f, 0.0f, 1.0f  // yellow
    };
    glGenBuffers(1, &sp.vbo);
    glBindBuffer(GL_ARRAY_BUFFER, sp.vbo);
    glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);
    glBindBuffer(GL_ARRAY_BUFFER, 0);

    glGenBuffers(1, &sp.ibo);
    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, sp.ibo);
    glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(indices), indices, GL_STATIC_DRAW);
    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0);
}

void setUniformLocation ( void )
{
    sp.projMatrLoc = glGetUniformLocation(sp.program, "projMatr");
}

void startShaderProg ( void )
{
    createBuffer();

    GLuint shaders[] = {
        createShader("vertex.glsl", GL_VERTEX_SHADER),
        createShader("fragment.glsl", GL_FRAGMENT_SHADER)
    };
    int len = sizeof(shaders) / sizeof(shaders[0]);
    createProgram(shaders, len);
    for (int i = 0; i < len; i++) {
        glDeleteShader(shaders[i]);
    }

    setUniformLocation();
    glEnable(GL_DEPTH_TEST);
    glDepthMask(GL_TRUE);
    glDepthFunc(GL_LEQUAL);
    glDepthRange(0.0f, 1.0f);
}

void _GLBuffer( void )
{
    glClearColor(0.0f, 0.0f, 1.0f, 0.0f);
    glClearDepth(1.0f);
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    glUseProgram(sp.program);

    glEnableVertexAttribArray(0);
    glEnableVertexAttribArray(1);
    glBindBuffer(GL_ARRAY_BUFFER, sp.vbo);
    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, sp.ibo);
    glVertexAttribPointer(0, 4, GL_FLOAT, GL_FALSE, 0, 0);
    glVertexAttribPointer(1, 4, GL_FLOAT, GL_FALSE, 0, (void *) (4*4*sizeof(float)));
    glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_SHORT, 0);
    glDisableVertexAttribArray(0);
    glDisableVertexAttribArray(1);

    glUseProgram(0);
}