Aero: How to draw solid (opaque) colors on glass?

Question

Using GDI+ to draw various colors:

brush = new SolidBrush(color);
graphics.FillRectangle(brush, x, y, width, height);

You\'ll notice that n

Answer 1

Do you want a stupid solution? Here you get a stupid solution. At least it's just one line of code. And causing a small but ignorable side effect.

Assumption

When drawing solid, right angle rectangles, GDI+ tends to speed things up by drawing them in a faster method than drawing other stuff. This technique is called bitbliting. That is actually pretty clever since it is the fastest way to draw rectangles on a surface. However, the rectangles to be drawn must fulfill the rule that they are right angled.

This clever optimization was done before there was DWM, Aero, Glass and all the new fancy stuff.

Internally, bitblitting just copies the RGBA color data of pixels from one memory area to another (so to say from your drawing on your window). Sadly enough, the RGB format it writes is incompatible with glass areas, resulting in the weird transparency effects you observed.

Solution

So here comes a twist. GDI+ can respect a transformation matrix, with which every drawing can be scaled, skewed, rotated or whatever. If we apply such a matrix, the rule that rectangles are right angled anymore is not guaranteed anymore. So, GDI+ will stop bitblitting these and draw them in a fashion similar to the ellipses.

But we also don't want to skew, scale or rotate our drawing. We simply apply the smallest transformation possible: We create a transformation matrix which moves every drawing down one pixel:

// If you don't get that matrix instance, ignore it, it's just boring math
e.Graphics.Transform = new Matrix(1f, 0.001f, 0f, 1f, 0f, 0f);

Now, bitblitting is off, rectangles are solid, violets are blue. If there would be just an easier way to control that, especially one not moving the drawings!

Thus said, if you want to draw on the first pixel row, use -1 as a Y coordinate.

You can decide if this really is a solution for you, or just ignore it.