libgdx, how to make opengl stretch the image correctly?

So I am trying to create a simple methode for stretching images when rendering them. But because opengl works with these triangles instead of rectangles it sort of screws up.

as you can see the 2 parts of the triangle are stretched differently. the code I have for this is the following:

public static void drawTexture(Texture texture, float x, float y, float x2, float y2, float x3, float y3, float x4, float y4){
    if(cantRender()) return;
    polyBatch.begin();
    float[] vertices = new float[20];

    float color = Color.WHITE.toFloatBits();
    int idx = 0;
    vertices[idx++] = x;
    vertices[idx++] = y;
    vertices[idx++] = color;
    vertices[idx++] = 0;
    vertices[idx++] = 1;

    vertices[idx++] = x2;
    vertices[idx++] = y2;
    vertices[idx++] = color;
    vertices[idx++] = 1;
    vertices[idx++] = 1;

    vertices[idx++] = x3;
    vertices[idx++] = y3;
    vertices[idx++] = color;
    vertices[idx++] = 1;
    vertices[idx++] = 0;

    vertices[idx++] = x4;
    vertices[idx++] = y4;
    vertices[idx++] = color;
    vertices[idx++] = 0;
    vertices[idx++] = 0;
    polyBatch.draw(texture, vertices, 0, 20);


    polyBatch.end();
}

Renderer.drawTexture(testTexture, 100, 100, 500, 100, 400, 500, 200, 500);

I have found a fix on the internet, but I don't know how i can make it work in combination with libgdx. this is the article i found: http://www.xyzw.us/~cass/qcoord/. The problem is that it doesn't seem like libgdx supports all 4 of these variables like described in the article.