我刚刚开始尝试使用OpenGL（使用freeglut和GLEW）。我可以弹出一个窗口，但是没有画任何东西，甚至无法改变背景颜色。
这是主要功能的样子：
int
main(int argc, char **argv)
{
GLenum err;
/* Initialize GLUT library */
glutInit(&argc, argv);
/* Set window mode */
glutInitDisplayMode(GLUT_RGBA | GLUT_DOUBLE);
/* Choose OpenGL version */
glutInitContextVersion(3, 3);
/* Choose OpenGL profile */
glutInitContextFlags(GLUT_CORE_PROFILE);
/* Create a GLUT window */
glutCreateWindow("OpenGL 2D");
/* Initialize GLEW library */
glewExperimental = GL_TRUE;
err = glewInit();
if(err != GLEW_OK) {
printf("Cannot initialize GLEW: %s\n",
glewGetErrorString(err));
return 1;
}
/* WORKAROUND: Ignore all GLEW errors */
while(glGetError() != GL_NO_ERROR)
;
(void) printf("OpenGL vendor: \"%s\"\n"
" renderer: \"%s\"\n"
" version: \"%s\"\n"
" SL version: \"%s\"\n",
glGetString(GL_VENDOR),
glGetString(GL_RENDERER),
glGetString(GL_VERSION),
glGetString(GL_SHADING_LANGUAGE_VERSION));
/* Set up callback function for "reshape" event */
printf("Setting callback functions\n");
glutReshapeFunc(canvas_reshape);
/* Set up callback function for "display" event */
glutDisplayFunc(canvas_display);
/* Set up callback function for "keyboard" event */
glutKeyboardFunc(canvas_keyboard);
/* Set up callback function for "timer" event */
glutTimerFunc(30, canvas_timer, 0);
/* Initialize OpenGL */
init();
/* Choose the window's position */
glutPositionWindow(100, 100);
/* Choose the window's size */
glutReshapeWindow(800, 600);
/* Start main loop */
printf("Entering main loop\n");
glutMainLoop();
return 0;
}
这是初始化的样子：
init()
{
const GLchar *vertex_shader_source[] = {
"#version 330 core\n",
"\n",
"layout(location=0) in vec4 position;\n",
"out vec4 color;\n",
"uniform mat4 viewtrans;\n",
"\n",
"void\n",
"main()\n",
"{\n",
" gl_Position = viewtrans * position;\n"
" color = vec4(1.0, 1.0, 1.0, 1.0);\n"
"}\n" };
const GLchar *fragment_shader_source[] = {
"#version 330 core\n",
"in vec4 color;\n",
"layout(location=0) out vec4 fcolor;\n",
"void\n",
"main()\n",
"{\n",
" fcolor = color;\n",
"}\n" };
char compiler_log[LOGSIZE];
/* Obtain an unused name for our vertex array */
printf("Creating vertex array\n");
glGenVertexArrays(1, &vertex_array);
check_error("glGenVertexArrays");
/* Tell OpenGL to use the new vertex array */
glBindVertexArray(vertex_array);
check_error("glBindVertexArray");
/* Obtain an unused name for our vertex buffer */
printf("Creating vertex buffer\n");
glGenBuffers(1, &vertex_buffer);
check_error("glGenBuffers");
/* Tell OpenGL to use the new vertex buffer as the
* vertex array */
glBindBuffer(GL_ARRAY_BUFFER, vertex_buffer);
check_error("glBindBuffer");
/* We want to get two coordinates from the vertex buffer and
* feed them as the first parameter to the vertex shader */
glEnableVertexAttribArray(0);
glVertexAttribPointer(0, 2, GL_FLOAT, GL_FALSE, sizeof(GLfloat) * 2, 0);
/* Create vertex shader */
printf("Creating vertex shader\n");
vertex_shader = glCreateShader(GL_VERTEX_SHADER);
check_error("glCreateShader");
/* Assign vertex shader source code */
glShaderSource(vertex_shader, sizeof(vertex_shader_source) / sizeof(GLchar *),
vertex_shader_source, 0);
check_error("glShaderSource");
/* Compile vertex shader */
glCompileShader(vertex_shader);
check_error("glCompileShader");
/* Get compiler log *//* Set up callback function for "timer" event */
glGetShaderInfoLog(vertex_shader, LOGSIZE, 0, compiler_log);
printf(" Compiler log: \"%s\"\n", compiler_log);
/* Create fragment shader */
printf("Creating fragment shader\n");
fragment_shader = glCreateShader(GL_FRAGMENT_SHADER);
check_error("glCreateShader");
/* Assign fragment shader source code */
glShaderSource(fragment_shader, sizeof(fragment_shader_source) / sizeof(GLchar *),
fragment_shader_source, 0);
check_error("glShaderSource");
/* Compile fragment shader */
glCompileShader(fragment_shader);
check_error("glCompileShader");
/* Get compiler log */
glGetShaderInfoLog(fragment_shader, LOGSIZE, 0, compiler_log);
printf(" Compiler log: \"%s\"\n", compiler_log);
/* Create shader program */
printf("Creating shader program\n");
shader_program = glCreateProgram();
check_error("glCreateProgram");
/* Attach vertex shader */
glAttachShader(shader_program, vertex_shader);
check_error("glAttachShader");
/* Attach fragment shader */
glAttachShader(shader_program, fragment_shader);
check_error("glAttachShader");
/* Link shader program */
glLinkProgram(shader_program);
check_error("glLinkProgram");
/* Get linker log */
glGetProgramInfoLog(shader_program, LOGSIZE, 0, compiler_log);
printf(" Linker log: \"%s\"\n", compiler_log);
/* Get location of "viewtrans" matrix */
viewtrans = glGetUniformLocation(shader_program, "viewtrans");
check_error("glGetUniformLocation");
/* Tell OpenGL to use the new shader program */
glUseProgram(shader_program);
/* Choose background color */
glClearColor(1.0, 0.0, 1.0, 0.0);
}
这是我用来绘制的内容：
static void
canvas_display()
{
glClearColor(0.0, 0.0, 0.0, 0.0);
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
}
全部基于教程。实际发生的事情是出现一个类似300 x 300的白色窗口，被重塑为800 x 600的黑色窗口，但是中间或角落仍然有一个300 x 300的白色正方形，其像素在部分情况下会变成黑色调整窗口大小，以便（手动或通过代码）消失正方形的一部分。我还编写了绘制三角形的代码，但这也不起作用，正如人们所期望的那样。但是无论如何，这是代码：
static void
canvas_display()
{
glClearColor(0.0, 0.0, 0.0, 0.0);
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
GLfloat vertices[] =
{ 0.0, 0.0,
0.5, 0.5,
0.5, 0.0 };
glGenVertexArrays(1, &vertex_array);
glBindVertexArray(vertex_array);
glGenBuffers(1, &vertex_buffer);
glBindBuffer(GL_ARRAY_BUFFER, vertex_buffer);
glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);
glEnableVertexAttribArray(0);
glVertexAttribPointer(0, 2, GL_FLOAT, GL_FALSE, sizeof(GL_FLOAT) * 2, vertices);
glDrawArrays(GL_TRIANGLES, 0, 3);
}
不要连续指定新的顶点数组对象。初始化时创建1 Vertex Array Object。顶点数组包含在Vertex Buffer Object中。当命名缓冲区对象绑定到ARRAY_BUFFER目标时，glVertexAttribPointer的最后一个参数将被视为缓冲区对象数据存储区中的字节偏移量。因此，偏移量必须为glVertexAttribPointer：
NULL确保在绘制几何图形时已安装程序并绑定了VAO。默认情况下，制服的值初始化为零。至少您必须先设置void init()
{
// [...]
GLfloat vertices[] =
{ 0.0, 0.0,
0.5, 0.5,
0.5, 0.0 };
glGenVertexArrays(1, &vertex_array);
glBindVertexArray(vertex_array);
glGenBuffers(1, &vertex_buffer);
glBindBuffer(GL_ARRAY_BUFFER, vertex_buffer);
glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);
glEnableVertexAttribArray(0);
glVertexAttribPointer(0, 2, GL_FLOAT, GL_FALSE, sizeof(GL_FLOAT) * 2, NULL);
}
，然后设置矩阵统一Identity matrix。由于您使用了双缓冲（viewtrans），因此在通过GLUT_DOUBLE
glutSwapBuffers