我很难获得要显示的屏幕外渲染纹理。我已经检查了网络和其他问题，显然遗漏了一些东西。
我是 OpenGL 的新手，所以很可能会犯一些幼稚的错误。这是使用着色器添加后期处理以将 firestor/secondlife viewer 项目修改为 equifisheye 投影的例程的一部分。我的测试代码基于使用 OpenGL 1.3 的 GLEW 和 GLUT 框架，因为查看器旨在在旧平台上运行。
方法是：
- 设置并初始化 FBO、渲染缓冲区和要绘制的纹理。
- 为绘制 glutCube 和 glutTeapot 初始化各种默认设置 :)
- 显示功能a）使用默认帧缓冲区绘制一个旋转立方体（工作正常）b）然后将纹理绘制到输出：全黑而不是旋转立方体。
我的代码是：
GLuint buffer_fbo;
GLuint bufferColtexture;
GLuint depthBuffer_rb;
typedef struct {
int width;
int height;
char* title;
float field_of_view_angle;
float z_near;
float z_far;
} glutWindow;
glutWindow win;
//
void ShutDown(void)
{
glDeleteFramebuffersEXT(1, &buffer_fbo);
glDeleteRenderbuffersEXT(1, &depthBuffer_rb);
glDeleteTextures(1,&bufferColtexture);
}
float g_potrotation = 0;
float g_potrotation_speed = 0.2f;
float xrot =0;
float yrot = 0;
float zrot = 0;
GLenum g_Drawbuffers[2] = {GL_COLOR_ATTACHMENT0_EXT };
void setupFBO(void)
{
// *********** set up scene FBO including dept buffers and their textures ****************
glGenFramebuffersEXT(1, &buffer_fbo);
// set up render buffers for depth info
glGenRenderbuffersEXT(1, &depthBuffer_rb);
glBindRenderbufferEXT(GL_RENDERBUFFER_EXT, depthBuffer_rb);
glRenderbufferStorageEXT(GL_RENDERBUFFER_EXT, GL_DEPTH_COMPONENT24, win.width, win.height);
// Genrate texture to render to
glGenTextures(1, &bufferColtexture);
glBindTexture(GL_TEXTURE_2D, bufferColtexture);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA8, win.width, win.height, 0, GL_RGBA, GL_UNSIGNED_BYTE, NULL);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
// attach texture to render to to fbo
glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, buffer_fbo);
glFramebufferTexture2DEXT(GL_FRAMEBUFFER_EXT, GL_COLOR_ATTACHMENT0_EXT, GL_TEXTURE_2D, bufferColtexture, 0);
glFramebufferRenderbufferEXT(GL_FRAMEBUFFER_EXT, GL_DEPTH_ATTACHMENT_EXT, GL_RENDERBUFFER_EXT, depthBuffer_rb);
GLenum status = glCheckFramebufferStatusEXT(GL_FRAMEBUFFER_EXT); // check frame buffer
if(status != GL_FRAMEBUFFER_COMPLETE_EXT)
{
printf("FRAMEBUFFER status error %i \n",status);
exit(1);
}
glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, 0); // bind back to default
}
void initialise()
{
setupFBO();
// select projection matrix
glMatrixMode(GL_PROJECTION);
// set the viewport
glViewport(0, 0, win.width, win.height);
// set matrix mode
glMatrixMode(GL_PROJECTION);
// reset projection matrix
glLoadIdentity();
GLfloat aspect = (GLfloat) win.width / win.height;
// set up a perspective projection matrix
gluPerspective(win.field_of_view_angle, aspect, win.z_near, win.z_far);
// specify which matrix is the current matrix
glMatrixMode(GL_MODELVIEW);
glShadeModel( GL_SMOOTH );
// specify the clear value for the depth buffer
glClearDepth( 1.0f );
glEnable( GL_DEPTH_TEST );
glDepthFunc( GL_LEQUAL );
// specify implementation-specific hints
glHint( GL_PERSPECTIVE_CORRECTION_HINT, GL_NICEST );
GLfloat amb_light[] = { 0.1, 0.1, 0.1, 1.0 };
GLfloat diffuse[] = { 0.6, 0.6, 0.6, 1 };
GLfloat specular[] = { 0.7, 0.7, 0.3, 1 };
glLightModelfv( GL_LIGHT_MODEL_AMBIENT, amb_light );
glLightfv( GL_LIGHT0, GL_DIFFUSE, diffuse );
glLightfv( GL_LIGHT0, GL_SPECULAR, specular );
glEnable( GL_LIGHT0 );
glEnable( GL_COLOR_MATERIAL );
glShadeModel( GL_SMOOTH );
glLightModeli( GL_LIGHT_MODEL_TWO_SIDE, GL_FALSE );
glDepthFunc( GL_LEQUAL );
glEnable( GL_DEPTH_TEST );
glEnable(GL_LIGHTING);
glEnable(GL_LIGHT0);
glClearColor(0.5, 0.5, 0.5, 1.0);
}
void drawquad(void)
{
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); // Clear The Screen And The Depth Buffer
glDisable(GL_LIGHTING); // This was the cause of the problem, disable lighting worked!
glLoadIdentity(); // Reset The View
glTranslatef(0.0f,0.0f,-5.0f);
glTranslatef(0.0f,0.0f,-5.0f);
glRotatef(xrot,1.0f,0.0f,0.0f);
glRotatef(yrot,0.0f,1.0f,0.0f);
glRotatef(zrot,0.0f,0.0f,1.0f);
glBindTexture(GL_TEXTURE_2D, bufferColtexture);
glBegin(GL_QUADS);
// Front Face
glTexCoord2f(0.0f, 0.0f); glVertex2f(-1.0f, -1.0f);
glTexCoord2f(1.0f, 0.0f); glVertex2f( 1.0f, -1.0f);
glTexCoord2f(1.0f, 1.0f); glVertex2f( 1.0f, 1.0f);
glTexCoord2f(0.0f, 1.0f); glVertex2f(-1.0f, 1.0f);
glEnd();
xrot+=0.3f;
yrot+=0.2f;
zrot+=0.4f;
glEnable(GL_LIGHTING); // now reenabling the lighting. after adding to fix code.
}
void display(void)
{
// set red background
// draw to fbo
glBindFramebufferEXT(GL_FRAMEBUFFER_EXT,0);
// Clear Screen and Depth Buffer
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glEnable(GL_TEXTURE_2D);
// set drawing a rotating cube as per default
glLoadIdentity();
// Define a viewing transformation
gluLookAt( 3,1,0, 0,0,0, 0,1,0);
// Push and pop the current matrix stack.
// This causes that translations and rotations on this matrix wont influence others.
glPushMatrix();
glColor3f(0,1,0);
glTranslatef(0,0,0);
glRotatef(g_potrotation,0,1,0);
glRotatef(90,0,1,0);
// Draw the solid cube
glutSolidCube(1);
glPopMatrix();
// draw teapot to fbo
glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, buffer_fbo);
glBindRenderbufferEXT(GL_RENDERBUFFER_EXT,depthBuffer_rb);
// Clear Screen and Depth Buffer
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glLoadIdentity();
// Define a viewing transformation
gluLookAt( 4,2,0, 0,0,0, 0,1,0);
// Push and pop the current matrix stack.
// This causes that translations and rotations on this matrix wont influence others.
glPushMatrix();
glColor3f(1,0,0);
glTranslatef(0,0,0);
glRotatef(g_potrotation,0,1,0);
glRotatef(90,0,1,0);
// Draw the teapot
glutSolidTeapot(1);
glPopMatrix();
g_potrotation += g_potrotation_speed;
glBindFramebufferEXT(GL_FRAMEBUFFER_EXT,0); // reset to default Frame and Render buffer
glBindRenderbufferEXT(GL_RENDERBUFFER_EXT,0);
drawquad();
glutSwapBuffers();
}
// informs OpenGL that window size has changed.
void reshape(int width, int height)
{
}
void idle(void)
{
glutPostRedisplay();
}
int checkglewOK()
{
if (GLEW_ARB_vertex_shader && GLEW_ARB_fragment_shader)
printf("Ready for GLSL\n");
else {
printf("Not totally ready :( \n");
exit(1);
};
}
void keyboard (unsigned char key, int mousePositionX, int mousePositionY)
{
switch (key)
{
case KEY_ESCAPE:
exit (0);
break;
default:
break;
}
}
int main(int argc, char** argv)
{
// set window values
win.width = 640;
win.height = 480;
win.title = "Shader Test";
win.field_of_view_angle = 45;
win.z_near = 1.0f;
win.z_far = 500.0f;
////////////////////////////////////////////////////////
// Initialise and Create Window
////////////////////////////////////////////////////////
glutInit(&argc, argv);
// set modes RGB-Alpha, doble bufferedd (prevent flickering)
// has a depth buffer to ensure that 3D object overlp OK
glutInitDisplayMode(GLUT_RGBA | GLUT_DOUBLE | GLUT_DEPTH); // set display mode
// define window size
glutInitWindowSize(win.width, win.height);
glutCreateWindow(win.title); // create the window
glewInit(); // Glew Init occurs after Create Window !!!
checkglewOK();
glutDisplayFunc(display); // register display function
//glutReshapeFunc(reshape); // register resize function
glutIdleFunc(idle); // register idel function
glutKeyboardFunc(keyboard);
initialise();
glutMainLoop(); // run glut main loop
ShutDown();
return EXIT_SUCCESS;
}