GDI+ application - change system coordinate origin

Question

Hello,

In my GDI+ application I create graphics (rectangles, circles and text) on the panel pnl. For graphical object I need to move the origin from top-left to bottom-left corner.
The solution is to apply consequently 2 transforms ScaleTransform and TranslateTransform to the Graphics object.

Graphics dc = pnl.CreateGraphics();
dc.ScaleTransform(1.0f, -1.0f);
dc.TranslateTransform(0.0f, -pnl.Height);

But in this way the text is mirrored !!!

Is there a simple way to resolve a problem?

Thanks in advance.

Pavel.

Nuno Pinto · Answer

You can use your own Point Structure to do that, i found this solution in other web site, I am not sure if i can mention the other web site, so I just post the code and say that it is from Jonathan C Dickinson. public struct FlippedPoint { public int X { get ; set ; } public int Y { get ; set ; } public FlippedPoint( int x, int y) : this () { X = x; Y = y; } public static implicit operator Point(FlippedPoint point) { return new Point(-point.X, -point.Y); } public static implicit operator FlippedPoint(Point point) { return new FlippedPoint(-point.X, -point.Y); } }

Pavel · Answer

Such solution will be difficult to manage because the positions of texts depends on thoses of shapes - for example I need to put numbers in the centers of circles. In anyway the coordinates 'y' of texts must be transformed: y -> "SOME CONST" - y. Probably I will decide to reject transforms and replace every y to pnl.Height - y . It's a pity, that such behaviour wasn't remarked by Microsoft engineers. Thank you once more for your assistance. Regards. Pavel.

Vulpes · Answer

That's right, they apply to all graphics drawn after the transformation is made. However, if you only have a few strings to draw, I'd suggest you draw them first before you change the origin to draw the shapes.

Pavel · Answer

But it seems, that transforms are applied to entire Graphics object, where everything is drawn - rectangles, circles and also text ... For shapes they are favourable, whereas for text not. Or there is some technique, allowing to selectly apply transforms ?

Vulpes · Answer

I was only proposing not to use the transform methods when drawing text. As you say, they work fine when drawing lines, shapes etc. For text, you'd need to do what you said and also subtract the height of the font being used.

Pavel · Answer

Thanks for response Vulpes. If I understood in right way, you propose to reject at all the using of transforms. If it is only solution, Ok ... I will proceed in this way. But I have plenty "geometric" graphics (rectangles, circles, etc.), that are correctly displayed with transforms, and only few "text" graphics. So, in order to consider bottom-left as origin, I should replace all "y" to "pnl.Height-y" ? Thanks. Pavel.

Vulpes · Answer

Yes, I've noticed previously that the methods which are supposed to change the graphics origin cause text to be inverted. I don't know of any solution to this except to stick with the origin at the top left corner and then draw the text at the appropriate location. So: Graphics dc = pnl.CreateGraphics(); // draw string from top left dc.DrawString("Pavel", drawFont, drawBrush, 0, 0); // draw string from bottom left dc.DrawString("Pavel", drawFont, drawBrush, 0, pnl.Height - drawFont.Height);

GDI+ application - change system coordinate origin

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