FBO -雪碧倒置版

Question

嗯，FBO的使用范围很广，它有助于使复杂的效果更容易。我设置FBO并绘制到它，然后渲染FBO纹理四，没有任何问题，甚至测试简单的屏幕处理彩色着色。但我给FBO的一切都因为某种原因被颠倒了。如果我渲染到股票屏幕FBO一切都是正常的，我甚至不执行任何旋转的雪碧。

FBO创建

typedef struct tex
{
 dim2i size; // int width, int height
 GLuint id;
} tex;

typedef struct fbo
{
 GLuint frame_buffer;
 tex buffer_tex;
}fbo;

void set_fbo(fbo* res, int width, int height)
{
 GLint tex_size;
 glGetIntegerv(GL_MAX_TEXTURE_SIZE, &tex_size);
 GLint render_buffer_size;
 glGetIntegerv(GL_MAX_RENDERBUFFER_SIZE, &render_buffer_size);
 LOGI("Max render buffer size: %d, max texture size: %d", render_buffer_size, tex_size);    //max render buffer size: 3838, max texture size: 2048
 glGenFramebuffers(1, &res->frame_buffer);
 GLuint depth_buffer;
 glGenRenderbuffers(1, &depth_buffer);
 glGenTextures(1, &res->buffer_tex.id);
 res->buffer_tex.size.w = width;
 res->buffer_tex.size.h = height;
 glBindTexture(GL_TEXTURE_2D, res->buffer_tex.id);
 glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, res->buffer_tex.size.w, res->buffer_tex.size.h, 0, GL_RGB, GL_UNSIGNED_BYTE, NULL);
 glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
 glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
 glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
 glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
 glBindRenderbuffer(GL_RENDERBUFFER, depth_buffer);
 glRenderbufferStorage(GL_RENDERBUFFER, GL_DEPTH_COMPONENT16, res->buffer_tex.size.w, res->buffer_tex.size.h);
 glBindFramebuffer(GL_FRAMEBUFFER, res->frame_buffer);
 glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, res->buffer_tex.id, 0);
 glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT, GL_RENDERBUFFER, depth_buffer);
 if(glCheckFramebufferStatus(GL_FRAMEBUFFER) == GL_FRAMEBUFFER_COMPLETE)
    LOGE("BUFFER OK");
 else
    LOGE("BUFFER NOT OK");
//BUFFER OK 
 glBindFramebuffer(GL_FRAMEBUFFER, 0);
 glBindTexture(GL_TEXTURE_2D, 0);
}

FBO使用

static fbo FBO;
static decor DECOR; //shield quad
static decor SCREEN_DECOR;// FBO textured quad

void on_surface_changed(int width, int height)
{
 set_fbo(&FBO, width, height);
 ...
}

void on_draw()
{
 glBindFramebuffer(GL_FRAMEBUFFER, FBO.frame_buffer);
 set_render_color(YELLOW); //glClearColor(...)
 glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
 draw_decor(&DECOR, get_shader(SPRITE_SIMPLE_SHADER), *get_proj(ORTHO_PROJ));
 glBindFramebuffer(GL_FRAMEBUFFER, 0);
 set_render_color(BLACK);
 glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
 draw_decor(&SCREEN_DECOR, get_shader(SPRITE_SIMPLE_SHADER), *get_proj(ORTHO_PROJ));
}

结果：

带有灰度着色器的结果：

​

不带FBO的呈现：

void on_draw_simple()
{
 set_render_color(YELLOW); //glClearColor(...)
 glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
 draw_decor(&DECOR, get_shader(SPRITE_SIMPLE_SHADER), *get_proj(ORTHO_PROJ));
}

​

​

Answer 1

从评论中汇总：

之所以会出现这种情况，是因为OpenGL的原点位于左下角，与大多数正在使用的窗口系统不同，后者的原点位于左上角。

只要确保纹理坐标从左上角的0,1到右下角的1,0，就可以正确地绘制FBO，或者用垂直翻转的纹理绘制四角体。