绘制到FBO - 精灵倒置上下问题

Question

那么,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并绘制它,然后渲染FBO纹理四边形,没有任何问题,甚至测试简单的屏幕处理颜色着色器.但是我为FBO渲染的一切都因为某些原因而颠倒过来.如果我渲染到库存屏幕FBO一切正常,我甚至不执行任何旋转精灵.

FBO创作

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用法

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: 灰度着色器的结果:

没有FBO渲染:

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

根据评论汇总：

发生这种情况是因为 OpenGL 的原点位于左下角，这与大多数使用的窗口系统的原点位于左上角不同。

只需确保纹理坐标从左上角的 0,1 到右下角的 1,0 即可正确绘制 FBO，或者绘制垂直翻转纹理的四边形。