Drawing Issues in OpenGL ES

Question

In my app, I have a red square (actually two triangles) that gets drawn onto the screen. However, if the user taps on the screen or moves their finger around, the drawing gets messed up and causes the square to start drawing in what seems to be random patterns. Any idea why this is happening? Code:

Triangle3D  *triangles = malloc(sizeof(Triangle3D) * 2);
triangles[0].v1 = Vertex3DMake(x, y, -3.0);
triangles[0].v2 = Vertex3DMake(x+1.0, y-1.0, -3.0);
triangles[0].v3 = Vertex3DMake(x-1.0, y-1.0, -3.0);
triangles[1].v1 = Vertex3DMake(x-1.0, y-1.0, -3.0);
triangles[1].v2 = Vertex3DMake(x+1.0, y-1.0, -3.0);
triangles[1].v3 = Vertex3DMake(x, y-2.0, -3.0);

    glLoadIdentity();

    glClearColor(0.7, 0.7, 0.7, 1.0);
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    glEnableClientState(GL_VERTEX_ARRAY);
    glColor4f(1.0, 0.0, 0.0, 1.0);
    glVertexPointer(3, GL_FLOAT, 0, triangles);
    glDrawArrays(GL_TRIANGLE_STRIP, 0, 18);
    glDisableClientState(GL_VERTEX_ARRAY);
    glClearColor(0.7, 0.7, 0.7, 1.0);

Answer 1

The Triangle Strip's vetcies should be arranged like this graph.

The other forms.

Answer 2

看起来你设置triangles[1].v1 3倍，而不是设置triangles[1].v1, v2, & v3 。