问使用glBlendFunc掩蔽，没有帧缓冲区

EN

glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGBA | GLUT_ALPHA | GLUT_DEPTH | GLUT_STENCIL);

GLdouble dRadius = 0.1; // Initial radius of spiral
GLdouble dAngle;        // Looping variable

// Use 0 for clear stencil, enable stencil test
glClearStencil(0);
glEnable(GL_STENCIL_TEST);

// Clear stencil buffer
glClear(GL_STENCIL_BUFFER_BIT);

// All drawing commands fail the stencil test, and are not
// drawn, but increment the value in the stencil buffer.
// glStencilFunc takes three arguments: the stencil function, the reference value, and the mask value. Whenever the stencil function is tested (for example GL_LESS), both the reference and the stencil value being tested from the buffer is bitwise ANDed with the mask: GL_LESS returns true if (ref & mask) < (stencil & mask).
glStencilFunc(GL_NEVER, 0x0, 0x0);
// glStencilOp takes three arguments: the stencil operation to call when the stencil test fails, the stencil operation to call when the stencil test passes but the depth test fails, and the stenciloperation to call when the stencil test passes AND the depth test passes (or depth test is disabled or no depth buffer is allocated).
glStencilOp(GL_INCR, GL_INCR, GL_INCR);

// Spiral pattern will create stencil pattern
// Draw the spiral pattern with white lines. We
// make the lines  white to demonstrate that the
// stencil function prevents them from being drawn
glColor3f(1.0f, 1.0f, 1.0f);
glBegin(GL_LINE_STRIP);
    for(dAngle = 0; dAngle < 400.0; dAngle += 0.1)
        {
        glVertex2d(dRadius * cos(dAngle), dRadius * sin(dAngle));
        dRadius *= 1.002;
        }
glEnd();

// Now, allow drawing, except where the stencil pattern is 0x1
// and do not make any further changes to the stencil buffer
glStencilFunc(GL_NOTEQUAL, 0x1, 0x1);
glStencilOp(GL_KEEP, GL_KEEP, GL_KEEP);

// Now draw red square
glColor3f(0.0f, 1.0f, 0.0f);
glRectf(0, 0, 200, 200);