Question

我的目标是能够在加载时缩放纹理，所以我不必在每次渲染精灵的帧上都这样做。我认为最好的方法是将缩放纹理渲染到另一个纹理上，基本上缓存它。但是，使用下面的代码，我只得到红色四边形（由于glClearColor）所以我知道FBO正在工作，而不是我渲染新纹理的方法

Texture *Graphics::loadTexture(const std::string& filename, int scale = 0) {
SDL_Surface *surface;
GLuint texture;

if((surface = IMG_Load(filename.c_str()))) {
    // Get the number of colors
    GLint numberOfColors = surface->format->BytesPerPixel;
    GLenum format;

    // Set the format of the texture based on the number of channels
    if(numberOfColors == 4) {
            if(surface->format->Rmask == 0x000000ff) {
                format = GL_RGBA;
            } else {
                format = GL_BGRA;
            }
    } else if(numberOfColors == 3) {
        if(surface->format->Rmask == 0x000000FF) {
            format = GL_RGB;
        } else {
            format = GL_BGR;
        }
    } else {
        throw Exception("Invalid image type for image  " + filename); 
    }

    // Generate texture id
    glGenTextures(1, &texture);

    // Bind the texture
    glBindTexture(GL_TEXTURE_2D, texture);

    // Texture stretching properties
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);

    // Create the image
    glTexImage2D(GL_TEXTURE_2D, 0, 4, surface->w, surface->h, 
                0, format, GL_UNSIGNED_BYTE, surface->pixels);

    glBindTexture(GL_TEXTURE_2D, 0);

} else {
    return NULL;
}
Texture *result;

if(scale > 1) {
    GLuint scaledTexture;
    GLuint fbo;
    GLuint fbod;

    // First we setup the depth buffer //
    // Create the framebuffer
    glGenRenderbuffersEXT(1, &fbod);

    // Bind the render buffer
    glBindRenderbufferEXT(GL_RENDERBUFFER_EXT, fbod);

    // Set the render buffer storage to be a depth component
    glRenderbufferStorageEXT(GL_RENDERBUFFER_EXT, GL_DEPTH_COMPONENT, surface->w*scale, surface->h*scale);

    // Set the render buffer of this buffer to the depth buffer
    glFramebufferRenderbufferEXT(GL_FRAMEBUFFER_EXT, GL_DEPTH_ATTACHMENT_EXT, GL_RENDERBUFFER_EXT, fbod);

    // Unbind the render buffer
    glBindRenderbufferEXT(GL_RENDERBUFFER_EXT, 0);

    // Next we setup the texture //
    glGenTextures(1, &scaledTexture);
    glBindTexture(GL_TEXTURE_2D, scaledTexture);
    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, surface->w*scale, surface->h*scale, 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);

    glBindTexture(GL_TEXTURE_2D, 0);

    // Setup the frame buffer //
    glGenFramebuffersEXT(1, &fbo);
    glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, fbo);

    // Attach the texture and render buffer to the frame buffer
    glFramebufferTexture2DEXT(GL_FRAMEBUFFER_EXT, GL_COLOR_ATTACHMENT0_EXT, GL_TEXTURE_2D,  scaledTexture, 0);

    // Attach the depth buffer
    glFramebufferRenderbufferEXT(GL_FRAMEBUFFER_EXT, GL_DEPTH_ATTACHMENT_EXT, GL_RENDERBUFFER_EXT, fbod);

    glPushAttrib(GL_VIEWPORT_BIT | GL_ENABLE_BIT);
    glViewport(0, 0, surface->w*scale, surface->h*scale);

    glLoadIdentity();

    glClearColor(1.0f, 0.0f, 0.0f, 1.0f);
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

    glBindTexture(GL_TEXTURE_2D, texture);

    glPushMatrix();

    glBegin(GL_QUADS);
        glTexCoord2i( 0, 0 );
        glVertex3f( 0.f, 0.f, 0.0f );

        glTexCoord2i( 1, 0 );
        glVertex3f( (GLfloat)surface->w*scale, 0.0f, 0.0f );

        glTexCoord2i( 1, 1 );
        glVertex3f( (GLfloat)surface->w*scale, (GLfloat)surface->h*scale, 0.f );

        glTexCoord2i( 0, 1 );
        glVertex3f( 0.0f, (GLfloat)surface->h*scale, 0.f );
    glEnd();

    glPopMatrix();


    glClearColor(0.0f, 0.0f, 0.0f, 1.0f);

    glPopAttrib();
    glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, 0);

    result = new Texture(scaledTexture, surface->w, surface->h);
} else {
    result = new Texture(texture, surface->w, surface->h);
}

//Texture *result = new Texture(texture, surface->w, surface->h);

if(surface) {
    SDL_FreeSurface(surface);
}

return result;
}

Answer 1

几条评论：

当你使用glLoadIdentity（）时，你知道你要重置哪个矩阵吗？使用glMatrixMode。
你的glPushMatrix（）/ glPopMatrix（）没用，因为你不修改它们之间的矩阵。
您确定已启用2D纹理吗？使用glEnable（GL_TEXTURE_2D）;

但无论如何，要清除两个矩阵，你应该在屏幕的右上角看到你的纹理（或者你正在使用生成的纹理的任何多边形）;你只需要修复UVs et Graphics :: loadTexture：

glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
glMatrixMode(GL_PROJECTION);
glLoadIdentity();

这应该可行，但我认为你应该在软件中进行扩展。

Answer 2

好吧，我决定做的不是在加载纹理时实现缩放，而是在sprite对象中实现它。因此，当我将顶点数据提交给GPU时，它会根据它的顶点缩放精灵，而不是缩放实际纹理。

Answer 3

如果没有试图告诉你该怎么做，而是告诉你最简单的方法来做你缩进的事（缩放纹理） - 答案是：

glBlitFramebuffer(sx0,sy0,sx1,sy1,dx0,dy0,dx1,dy1, GL_COLOR_BUFFER_BIT, GL_LINEAR)

如果尺寸不匹配，它将自动缩放读取的图像为了使其工作，你应该为每个人设置GL_READ_FRAMEBUFFER，GL_DRAW_FRAMEBUFFER和glDrawBuffer（）。

使用Framebuffer缩放纹理

3 个答案: