scaling image with anchor point

scaling image with anchor point

void testApp::setup()
{
    img.loadImage("history.png");
    ofSetWindowShape(img.getWidth(), img.getHeight());
    scale = 1.0;
}

void testApp::update()
{
    
}

void testApp::draw()
{
    mtrx.makeIdentityMatrix();
    mtrx.scale(scale, scale, scale);
    mtrx.translate(-imagePoint*(scale-1));
    mtrx.translate((touchBeginPoint - imagePoint));
    ofPushMatrix();
    ofMultMatrix(mtrx);
    img.draw(0, 0);
    ofPopMatrix();
}

void testApp::keyPressed(int key)
{
    if (key == 'a' && scale < 5.0)
        scale += 0.1;
    else if (key == 's' && scale - 0.1 >= 1.0)
        scale -= 0.1;
}

void testApp::mousePressed(int x, int y, int button)
{
    imagePoint = (ofPoint(x, y) - mtrx.getTranslation()) / scale; //画像の相対座標でのポイント
    touchBeginPoint = ofPoint(x, y);//screenのポイント
}