I'm working on a color selector in C# for a particle emitter for a game. Users select a start min and max color, and an end min and max color, and I draw a quad representing those four colors, and all the possible values in between. At present I'm using a PathGradientBrush, and set four points up as the path, and assign colors to each of them. The problem I'm having is a visual artifact: a line that runs along the diagonal of the resultant image. Visual artifact No artifact going in the other direction, though: I know why the artifact appears. It has to do with where the "center" is. Right now I'm setting the center point to the upper left corner, as it minimizes the artifact (only shows up in one direction). I'm not sure how to remove it entirely though. Ideally I'd like something that looks like a quad in DirectX or OpenGL. (clicky), but I can't figure out how to get there. I've tried looking on sites that do C# graphics tutorials, but they all seem to have that same artifact. Here's the code I'm using to set up the PathGradientBrush: Any ideas people have would be appreciated.

You need a better anti-aliasing filter... does the PathGradientBrush have any quality properties? You need to enable bilinear filtering, it looks like it's using nearest-neighbor.

Trying setting Graphics.InterpolationMode to high quality.

I tried various settings of interpolation mode but none of them have any noticable effect. I don't think this is an aliasing issue. I've seen it in pretty much every tutorial or article with pictures that talks about the pathgradientbrush. More and more I'm thinking it's a logical flaw in the way the brush interpolates between the center and it's edges.

At the moment I'm thinking of doing a four pass drawing using four linear gradient brushes. One would interpolate for each edge, and the results would be alpha blended. So if I had a square that looked like this:

R-G| |B-W

with R = red, G = green, B = blue, W = white, you'd do a base layer that was a Red to Blue, then a layer of Green to white, with alpha fading to 0 as it moved left. Then do the same along the vertical direction. Hope I've explained it well.

Two reasons for not using the color dialog:

1. My custom control needs to show four user selected colors being Lerped together. The color dialog wasn't built for that.

2. My team got fed up with the default color dialog, so we built our own :P

Likewise a prebuilt bitmap wouldn't work because the four colors need to be selected at run time. I have, however, also tried outputting to a small bitmap and scaling the bitmap, but while the result is smooth it's a far cry from a true Lerp of the four colors. SetPixel is possible too, but I'm trying to avoid something so brute force.

Thanks, but I did actually write my own little control to select a single color graphically using hue, sat, and lum. The problem here is that I have potentially four unique colors in the four corners, meaning that I need some way to bilinearly interpolate between those four colors quickly. And these four colors need to be determinable at run time from the user.

Basically, the user selects the upper left corner, and a dialog pops up, asking for a color choice (where either the default C# colordialog could be used, or a custom color control). Once the user selects a color, the control updates itself and that corner becomes the new color.

I got a hacky solution up right now, where I just brute force the bilinear calculation and SetPixel for each pixel. It takes about a second to draw, so it's something I could live with, but a more manageable draw time would be nice, too.