我仍然无法追踪问题出在哪里，但在重构我的代码后，一切似乎都呈现得很好。不管怎样，这里是渲染离屏图像的完整代码：
实际的 draw_my_scene() 被省略了，因为它在此上下文中不相关
void bind_frame(GLuint * texture, int width, int height){
static int _width, _height;
static int _state;
static GLuint framebuffer, color_attachment;
if(_width != width || _height != height) _state = 1;
if(_state == 1){ // = 1 recreate resources
if(width < 1 || height < 1) printf("error offscreen width or height is less than 1
");
// delete if necessery
opengl_delete_texture(texture);
opengl_delete_framebuffer(&framebuffer);
// texture
opengl_create_texture(&color_attachment, width, height, GL_RGBA8);
opengl_texture_tile_no_repeat(color_attachment);
opengl_texture_filter_smooth(color_attachment);
// framebuffer
opengl_create_framebuffer(&framebuffer, width, height);
opengl_framebuffer_color(framebuffer, color_attachment);
_width = width, _height = height;
_state = 0;
}
// prepare frame for drawing
glBindFramebuffer(GL_DRAW_FRAMEBUFFER, framebuffer);
glViewport(0, 0, width, height);
*texture = color_attachment;
}
void draw_frame(GLuint frame, mat4 transform){
static GLuint vertex_array, vertex_buffer, index_buffer,
program,
texture_loc, model_loc;
static int _state = 1;
if(_state == 1){
// attributes
int num_of_attribs = 2;
int location [] = {0, 1};
int count [] = {2, 2};
int offset [] = {0, 2};
int binding [] = {0, 0};
// vertex_array
opengl_create_vertex_array(&vertex_array);
for(int i = 0; i < num_of_attribs; i++){
opengl_vertex_array_enable_attrib(vertex_array, location[i], GL_FLOAT, sizeof(float)*count[i], count[i], offset[i], binding[i]);
}
// vertex_data
const float vertex_data[] = {
// pos tex
-1.0f, -1.0f, 0.0f, 0.0f,
-1.0f, 1.0f, 0.0f, 1.0f,
1.0f, -1.0f, 1.0f, 0.0f,
1.0f, 1.0f, 1.0f, 1.0f
};
// vertex_buffer
opengl_create_buffer(&vertex_buffer, (void*)&vertex_data, sizeof(vertex_data));
opengl_vertex_array_vertex_buffer(vertex_array, vertex_buffer, 0, sizeof(float)*4, 0);
// index_buffer
const int index_data[] = {0, 1, 2, 1, 3, 2};
opengl_create_buffer(&index_buffer, (void*)&index_data, sizeof(index_data));
opengl_vertex_array_element_buffer(vertex_array, index_buffer);
// vertex_shader_code
static const char * vertex_shader_code =
"#version 460 core
"
"uniform mat4 model;
"
"layout (location = 0) in vec2 vPos;
"
"layout (location = 1) in vec2 vTexCoord;
"
"out vec2 texCoord;
"
"void main()
"
"{
"
// "gl_Position = vec4(vPos, 0.0, 1.0);
"
"gl_Position = model * vec4(vPos, 0.0, 1.0);
"
// "texCoord = vTexCoord * vec2(1.0, -1.0);
" // flip y
"texCoord = vTexCoord;
"
"}
";
// fragment_shader_code
static const char * fragment_shader_code =
"#version 460 core
"
"uniform sampler2D tex;
"
"in vec2 texCoord;
"
"out vec4 FragColor;
"
"void main(){
"
"FragColor = texture(tex, texCoord);
"
"}
";
// vertex & fragment shaders
GLuint vertex_shader, fragment_shader;
opengl_compile_shader(&vertex_shader, GL_VERTEX_SHADER, vertex_shader_code);
opengl_compile_shader(&fragment_shader, GL_FRAGMENT_SHADER, fragment_shader_code);
// program
opengl_create_program(&program, vertex_shader, fragment_shader);
// uniform location
texture_loc = glGetUniformLocation(program, "tex");
model_loc = glGetUniformLocation(program, "model");
_state = 0;
}
glBindTextureUnit(1, frame);
glUseProgram(program);
glUniform1i(texture_loc, 1);
glUniformMatrix4fv(model_loc, 1, GL_FALSE, (const GLfloat*)transform);
glBindVertexArray(vertex_array);
glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, (void*)0);
}
int main(){
if(glfw_create_window_opengl(512, 512)) return -1;
if(opengl_init()) return -1;
// glEnable(GL_MULTISAMPLE);
// glPolygonMode(GL_FRONT_AND_BACK, GL_LINE);
// glPolygonMode(GL_FRONT_AND_BACK, GL_POINT);
// glPolygonMode(GL_FRONT_AND_BACK, GL_TRIANGLES);
// glEnable(GL_DEPTH_TEST); // this one fixes assimp models displaying incorrectly (wrong z-buffer)
// glEnable(GL_CULL_FACE);
// glDisable(GL_CULL_FACE);
// glCullFace(GL_BACK);
// glCullFace(GL_FRONT);
// glFrontFace(GL_CW); // clockwise
// glFrontFace(GL_CCW); // counter-clockwise - default
// glEnable(GL_SCISSOR_TEST);
GLuint frame0;
mat4 frame0_transform;
glm_mat4_identity(frame0_transform);
while(!glfw_window_should_close()){
int w, h;
glfw_get_frame_size(&w, &h);
glViewport(0, 0, w, h);
glClearColor(0.0f, 0.0f, 0.0f, 0.0f);
glClear(GL_COLOR_BUFFER_BIT);
bind_frame(&frame0, 128, 128);
// draw everything as usual
draw_my_scene();
glBindFramebuffer(GL_DRAW_FRAMEBUFFER, 0);
draw_frame(frame0, frame0_transform);
glfw_swap_buffers();
glfw_poll_events();
}
opengl_quit(); // free gl resources
glfw_quit();
return 0;
}