c++ - 将缓冲区内容返回到 OpenGL 中的纹理

Question

为了让我的迷宫类游戏更快，我决定将我绘制的球放在纹理中，因为我必须为每个房间绘制一次，并且我使用模板缓冲区将其绘制为凹多边形，这需要更多时间比使用纹理。问题是，当我渲染游戏开始后的第三帧时，我从后台缓冲区正确地将它放入纹理中，我的问题是，为什么会这样？

当我使用 thirst frame 的纹理时，我的纹理是纯白色的，所以里面什么都没有。当我使用第二帧的纹理时，我只有所需纹理的黑色背景，而当我使用第三帧的纹理时，我就有了所需的纹理。对于帧计数，我在“drawTexture”函数中使用静态变量“done”。

从第一帧复制:

从第二帧复制:

从第三帧复制(期望的结果):

void DrawBall::drawTexture(float imageD) {
    static int done = 0;

    if (done < 3) {
        drawToTexture(imageD);
        done++;
    }

    glEnable(GL_TEXTURE_2D);
    glBindTexture (GL_TEXTURE_2D, texture);

    glColor3f(1, 1, 1);
    glBegin (GL_QUADS);
        glTexCoord2f (0.0, 0.0); glVertex3f (0.0, 0.0, -imageD);    
        glTexCoord2f (1.0, 0.0); glVertex3f (5.0, 0.0, -imageD);
        glTexCoord2f (1.0, 1.0); glVertex3f (5.0, 5.0, -imageD);    
        glTexCoord2f (0.0, 1.0); glVertex3f (0.0, 5.0, -imageD);
    glEnd ();

    glDisable(GL_TEXTURE_2D);   
}

void DrawBall::drawToTexture(float imageD) {
    int viewport[4];
    glGetIntegerv(GL_VIEWPORT, (int*) viewport);

    int textureWidth = 64;
    int textureHeight = 64;

    texture = genEmptyTexture(textureWidth, textureHeight);

    glViewport(0, 0, textureWidth, textureHeight);
    glMatrixMode(GL_PROJECTION);                            
    glLoadIdentity();                                       
    gluPerspective(45.0f, 1, 1, 100);
    glMatrixMode(GL_MODELVIEW);                         
    glLoadIdentity();                                       

    /* 
       This function calculates the vertexes for the ball
       inside a vector<vector<float>> variable "test"
    */
    _calculateCircleVertexes(0.0f, 0.0f, -2.0f, 0.249f, &test, 20);

    _displayBall(&test, 0.0f, 0.0f, 0.5f, -2.0f, &*smallBallColor);

    glBindTexture(GL_TEXTURE_2D, texture);
    glCopyTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, 0, 0, textureWidth, textureHeight, 0);

    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT | GL_STENCIL_BUFFER_BIT);

    glViewport(viewport[0], viewport[1], viewport[2], viewport[3]);
    glMatrixMode(GL_PROJECTION);    
    glLoadIdentity();               
    gluPerspective(45.0f, (GLfloat)viewport[2] / (GLfloat)viewport[3], 1.0f, imageD + 10.0f);
    glMatrixMode(GL_MODELVIEW);     
    glLoadIdentity();   
}

GLuint DrawBall::genEmptyTexture(unsigned int width, unsigned int height) {
    GLuint txtIndex;

    glGenTextures(1, &txtIndex);                                    
    glBindTexture(GL_TEXTURE_2D, txtIndex);                         

    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, width, height, 0,
    GL_RGB, GL_UNSIGNED_BYTE, NULL);                            

    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
    glTexParameteri (GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
    glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MIN_FILTER,GL_LINEAR);
    glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MAG_FILTER,GL_LINEAR);

    return txtIndex;
}

void DrawBall::_displayBall(vector<vector<GLfloat>> *vertexes, GLfloat x, GLfloat y
                        , GLfloat imageW, GLfloat imageD, color *color) {
    glTranslatef(x, y, imageD);

    glClearStencil(0);
    glColorMask(GL_FALSE, GL_FALSE, GL_FALSE, GL_FALSE);
    glEnable(GL_STENCIL_TEST);
    glStencilFunc(GL_NEVER, 0, 1);
    glStencilOp(GL_INVERT, GL_INVERT, GL_INVERT);

    glBegin(GL_POLYGON);
        vector<vector<GLfloat>>::iterator it = vertexes->begin();
        for (; it != vertexes->end(); it++) {
            glVertex3f((*it)[0], (*it)[1], 0.0f);
        }
    glEnd();

    glColorMask(GL_TRUE, GL_TRUE, GL_TRUE, GL_TRUE);
    glStencilFunc(GL_EQUAL, 1, 1);
    glStencilOp(GL_ZERO, GL_ZERO, GL_ZERO);

    glColor3f(color->r, color->g, color->b);
    glBegin(GL_QUADS);
        glVertex3f(-(imageW / 2.0f), -(imageW / 2.0f), 0.0f);
        glVertex3f( (imageW / 2.0f), -(imageW / 2.0f), 0.0f);
        glVertex3f( (imageW / 2.0f),  (imageW / 2.0f), 0.0f);
        glVertex3f(-(imageW / 2.0f),  (imageW / 2.0f), 0.0f);
    glEnd();

    glDisable(GL_STENCIL_TEST);

    glTranslatef(x, y, -imageD);
}

Answer 1

您不应该使用窗口帧缓冲区(包括后台和前台缓冲区)进行渲染到纹理操作。它很容易破裂(您已经体验过)。而是使用所谓的 Framebuffer 对象，并将纹理作为渲染目标。