How to paint a precise Gradient with LinearGradientBrush in C#?

Question

Hi,

I'm painting this object in C# using GDI and I need to have precise pixel painting. However, this is not working... I don't know if it matters but the object I'm painting is a ToolStrip, I'm doing a custom ToolStrip render.

I drew a horizontal blue line at y-pixel 1, than a yellow one at y-pixel 2 than a red one at y-pixel 3. These are not real colors it's just for me to see better.

Like this:

Color cTop1 = Color.FromArgb(255, Color.Blue);
Color cTop2 = Color.FromArgb(255, Color.Yellow);
Color cTop3 = Color.FromArgb(255, Color.Red);

g.DrawLine(new Pen(cTop1), 0, 1, aBounds.Width, 1);
g.DrawLine(new Pen(cTop2), 0, 2, aBounds.Width, 2);
g.DrawLine(new Pen(cTop3), 0, 3, aBounds.Width, 3);

Than, at y-pixel 4 I started filling a rectangle with the LinearGradientBrush like this:

Rectangle rTop = new Rectangle(0, 3, aBounds.Width, (aBounds.Height / 2) - 4);

Color cTop = Color.FromArgb(245, Color.White);
Color cBottom = Color.FromArgb(222, Color.White);

LinearGradientBrush tGradient = new LinearGradientBrush(rTop, cTop, cBottom, LinearGradientMode.Vertical);
g.FillRectangle(tGradient, rTop);

The problem is that the gradient is painting above the red line. The blue and yellow ones are ok, but the red line, which should be RGB=255,0,0, it's in fact RGB=255,111,111.

I can't understand why... I've played in SmoothingMode, InterpolationMode, CompositionMode, CompositionQuality but I just can't make it right...

Any ideias?

Answer 1

It's possible that the brush is being wrapped and what you are seeying is the oposite colour "bleeding" in.

Try and set the wrapmode to

brush.WrapMode = Drawing2D.WrapMode.TileFlipXY