Gradients are beautiful, have always been so and will continue being beautiful. Oops! What am I doing here? I guess I got carried away a little. Pardon me. Well seriously speaking, there are times when it would be nice to have a gradient background for our windows. I think the first time I remember seeing gradients was in the Setup programs generated by Install Shield. Even during the Windows 3.11 days, they had Setup programs that typically used a Blue gradient as their background. And recently while I have been making CP stats using PowerPoint, I use an Orange gradient as my presentation's background. Well creating gradients is not a big deal as I found out.
This one uses two dark colors to create the gradient effect
This one uses green and white as the two border colors and a gradient is filled smoothly between these colors
Well, all you need to do is to override
OnEraseBkgnd in your
CWnd class. We start with one color and slowly change the RGB values till we end up with the other color. It's basically mathematics and I am not really good at maths. So the algorithm I have used might not be perfect and I apologize to you for that. But it portrays how to get a gradient effect which is what I wanted. If better mathematicians than me can give me an easier formula I'd be very happy about that.
int r1=127,g1=127,b1=56; int r2=5,g2=55,b2=165;
r = r1 + (i * (r2-r1) / rect.Width());
g = g1 + (i * (g2-g1) / rect.Width());
b = b1 + (i * (b2-b1) / rect.Width());
I use a black to red gradient here
This uses two fluorescent colors and I don't recommend this sort of combination as it hurts the eyes
Similar to the horizontal gradient we override
int r1=127,g1=127,b1=56; int r2=5,g2=55,b2=165;
r = r1 + (i * (r2-r1) / rect.Height());
g = g1 + (i * (g2-g1) / rect.Height());
b = b1 + (i * (b2-b1) / rect.Height());
A beautiful bluish gradient. Just like those Installshield backgrounds
Pink, for the *ahem* ladies here :-)
Diagonal gradients are slightly tricky. Unlike horizontal and vertical gradients we are not handling rectangles here. So we will not be able to use
FillSolidRect for our purpose. In fact we need to use
LineTo in a rather heavy loop. Being a novice at this GDI stuff, I put all my code in
OnEraseBkgnd. The painting was so slow that it almost seemed like an animation. I was disappointed to say the least. That's when some of the gurus here suggested that I use a memory DC. So I used
CreateCompatibleDC to create a memory DC and drew directly onto this DC. Then I used
BitBlt to blast it into the actual DC. Well, there was considerable improvement. Now the animation effect was gone. But still there was a very noticeable flicker. This was really bad. But there was too much looping in the painting code. That's when I got this idea of keeping a
CBitmap member. During initialization I'll draw all my gradient stuff into this
CBitmap. Now all I needed to do in
OnEraseBkgnd was to
BitBlt this bitmap into the DC and voila, things were fast and smooth once again.
And I wrote a function called
MakeBitmap which creates the gradient bitmap and puts it into our
CBitmap member. In my dialog based application I called
OnInitDialog. In your SDI programs I guess you are supposed to call
while(x1 < rect.Width() && y1 < rect.Height())
if(y1 < rect.Height()-1)
if(x2 < rect.Width()-1)
int i = x1+y1;
r = r1 + (i * (r2-r1) / (rect.Width()+rect.Height()));
g = g1 + (i * (g2-g1) / (rect.Width()+rect.Height()));
b = b1 + (i * (b2-b1) / (rect.Width()+rect.Height()));
CPen *oldpen = dc2.SelectObject(&p);
All the screenshots in this article have been resized using Adobe Photoshop 6 and I'd like to thank Ravi Bhavnani for his image resizing tips.
Nish is a real nice guy who has been writing code since 1990 when he first got his hands on an 8088 with 640 KB RAM. Originally from sunny Trivandrum in India, he has been living in various places over the past few years and often thinks it’s time he settled down somewhere.
Nish has been a Microsoft Visual C++ MVP since October, 2002 - awfully nice of Microsoft, he thinks. He maintains an MVP tips and tricks web site - www.voidnish.com
where you can find a consolidated list of his articles, writings and ideas on VC++, MFC, .NET and C++/CLI. Oh, and you might want to check out his blog on C++/CLI, MFC, .NET and a lot of other stuff - blog.voidnish.com
Nish loves reading Science Fiction, P G Wodehouse and Agatha Christie, and also fancies himself to be a decent writer of sorts. He has authored a romantic comedy Summer Love and Some more Cricket
as well as a programming book – Extending MFC applications with the .NET Framework
Nish's latest book C++/CLI in Action
published by Manning Publications is now available for purchase. You can read more about the book on his blog.
Despite his wife's attempts to get him into cooking, his best effort so far has been a badly done omelette. Some day, he hopes to be a good cook, and to cook a tasty dinner for his wife.