理解glPushMatrix()和glPopMatrix()

Question

我有以下代码:

void drawObj1(){    
    glPushMatrix();
            glTranslatef(rBaseInitPos + (rBaseDim[0] / 2), rBaseDim[1] + baseIncrement + rBaseDim[1] / 2, rBaseDim[2] / 2);
            glRotatef(rBaseArmRotateAngle, 0, 1, 0);
            /*
                    glPushMatrix();
    */
            drawRobotBaseArm();
            /*
                    glPopMatrix();
    */
            glPushMatrix();
                glRotatef(90, 1, 0, 0);
                glEnable(GL_TEXTURE_2D);
                glBindTexture(GL_TEXTURE_2D, rCamouflage[0]);
                gluQuadricTexture(obj, GL_TRUE);
                gluQuadricDrawStyle(obj, GLU_FILL);
                gluDisk(obj, 0, (rBaseDim[0] / 2) - 0.5, 16, 4);
                gluCylinder(obj, (rBaseDim[0] / 2) - 0.5, (rBaseDim[0] / 2) - 0.5, rBaseDim[1] / 2, 16, 4);
                glDisable(GL_TEXTURE_2D);
            glPopMatrix();                      
        glPopMatrix();
    }


void drawScene(){
    glTranslatef(X, Y, Z);
    drawObj0();
    drawObj1();
}

使用上面的代码,因为在内部和 内部drawRobotBaseArm();都有一个翻译也被翻译.由于我不想这样,我已经取消了对代码的注释DiskCylinderdrawRobotBaseArm();

这样做,代码如下:

glTranslatef(rBaseInitPos + (rBaseDim[0] / 2), rBaseDim[1] + baseIncrement + rBaseDim[1] / 2, rBaseDim[2] / 2);
glRotatef(rBaseArmRotateAngle, 0, 1, 0);

只有作用于drawRobotBaseArm();现在的Disk和 Cylinder不平移和旋转.

我似乎无法理解如何glPushMatrix()和glPopMatrix()工作.任何想法我怎样才能实现我正在寻找的东西？

Answer 1

(请注意,在OpenGL 3.1+中不推荐使用这些函数并将其删除.如果您正在处理一个严肃的项目,请考虑切换到像GLM这样的专用数学库.)

OpenGL保留一堆矩阵以快速应用和删除转换.glPushMatrix复制顶部矩阵并将其推入堆栈,同时glPopMatrix将顶部矩阵从堆栈中弹出.所有变换函数(glScaled等)在顶部矩阵上起作用,顶部矩阵是所有渲染命令用于变换其数据的内容.

通过推送和弹出矩阵,您可以控制哪些转换适用于哪些对象,以及将转换应用于对象组,并轻松反转转换,以便它们不会影响其他对象.

一个例子:

glPushMatrix();          // Creates matrix 1 on the top
glTranslated(100, 0, 0); // Applies translation to matrix 1

drawSphere();            // Draws a sphere with translation <100, 0, 0>

glPushMatrix();          // Clones matrix 1 to create matrix 2 and pushes it on the top.
glScaled(2,2,2);         // Scales matrix 2; doesn't touch matrix 1

drawSphere();            // Draws a sphere with both translation <100, 0, 0> and scale <2,2,2>

glPopMatrix();           // Deletes matrix 2; matrix 1 becomes the top.

drawSphere();            // Same as the first sphere.

glPopMarix();            // Deletes matrix 1

在你的例子中,做glPush/PopMatrix左右drawRobotBaseArm意味着完成的变换在被drawRobotBaseArm调用之后被反转,因此它们不会影响任何其他对象.