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Using color gradients as backgrounds in your dialogs and views

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9 Jun 2002CPOL3 min read 300.6K   93   53
Beginner article that shows how you can create horizontal, vertical and diagonal backgrounds. Also tells you what to watch out for, to avoid flickering when doing complicated drawing.

Gradients

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.

Horizontal gradients

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.

CDialog::OnEraseBkgnd(pDC);

CRect rect;
GetClientRect(&rect);

int r1=127,g1=127,b1=56; //Any start color
int r2=5,g2=55,b2=165; //Any stop color

for(int i=0;i<rect.Width();i++)
{ 
    int r,g,b;
    r = r1 + (i * (r2-r1) / rect.Width());
    g = g1 + (i * (g2-g1) / rect.Width());
    b = b1 + (i * (b2-b1) / rect.Width());
    pDC->FillSolidRect(i,0,1,rect.Height(),RGB(r,g,b));
}


return true;

Vertical gradients

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 OnEraseBkgnd

CDialog::OnEraseBkgnd(pDC);

CRect rect;
GetClientRect(&rect);

int r1=127,g1=127,b1=56; //Any start color
int r2=5,g2=55,b2=165; //Any stop color

for(int i=0;i<rect.Height();i++)
{ 
    int r,g,b;
    r = r1 + (i * (r2-r1) / rect.Height());
    g = g1 + (i * (g2-g1) / rect.Height());
    b = b1 + (i * (b2-b1) / rect.Height());
    pDC->FillSolidRect(0,i,rect.Width(),1,RGB(r,g,b));
}


return true;

Diagonal gradients

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 MoveTo and 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.

CDialog::OnEraseBkgnd(pDC);

CRect rect;
GetClientRect(&rect);

CDC dc2;
dc2.CreateCompatibleDC(pDC);
CBitmap *oldbmap=dc2.SelectObject(&m_bitmap);

/*We copy the bitmap into the DC*/ 
pDC->BitBlt(0,0,rect.Width(),rect.Height(),&dc2,0,0,SRCCOPY);
dc2.SelectObject(oldbmap);

return true;

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 MakeBitmap inside OnInitDialog. In your SDI programs I guess you are supposed to call MakeBitmap inside OnInitialUpdate.

void CYourClassName::MakeBitmap()
{
    CPaintDC dc(this);
    CRect rect;
    GetClientRect(&rect);

    int r1=245,g1=190,b1=240;
    int r2=130,g2=0,b2=0;

    int x1=0,y1=0;
    int x2=0,y2=0;

    CDC dc2;
    dc2.CreateCompatibleDC(&dc);

    if(m_bitmap.m_hObject)
        m_bitmap.DeleteObject();
    m_bitmap.CreateCompatibleBitmap(&dc,rect.Width(),
        rect.Height());

    CBitmap *oldbmap=dc2.SelectObject(&m_bitmap);

    while(x1 < rect.Width() && y1 < rect.Height())
    {
        if(y1 < rect.Height()-1)
            y1++;
        else
            x1++;

        if(x2 < rect.Width()-1)
            x2++;
        else
            y2++;

        int r,g,b;
        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 p(PS_SOLID,1,RGB(r,g,b));
        CPen *oldpen = dc2.SelectObject(&p); 

        dc2.MoveTo(x1,y1);
        dc2.LineTo(x2,y2);

        dc2.SelectObject(oldpen);
    } 

    dc2.SelectObject(oldbmap);

}

Conclusion

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.

License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)


Written By
United States United States
Nish Nishant is a technology enthusiast from Columbus, Ohio. He has over 20 years of software industry experience in various roles including Chief Technology Officer, Senior Solution Architect, Lead Software Architect, Principal Software Engineer, and Engineering/Architecture Team Leader. Nish is a 14-time recipient of the Microsoft Visual C++ MVP Award.

Nish authored C++/CLI in Action for Manning Publications in 2005, and co-authored Extending MFC Applications with the .NET Framework for Addison Wesley in 2003. In addition, he has over 140 published technology articles on CodeProject.com and another 250+ blog articles on his WordPress blog. Nish is experienced in technology leadership, solution architecture, software architecture, cloud development (AWS and Azure), REST services, software engineering best practices, CI/CD, mentoring, and directing all stages of software development.

Nish's Technology Blog : voidnish.wordpress.com

Comments and Discussions

 
GeneralRe: GDI+ Pin
Rama Krishna Vavilala10-Jun-02 1:36
Rama Krishna Vavilala10-Jun-02 1:36 
GeneralRe: GDI+ Pin
Nish Nishant10-Jun-02 1:28
sitebuilderNish Nishant10-Jun-02 1:28 
GeneralRe: GDI+ Pin
Alex Cramer17-Jun-02 16:42
Alex Cramer17-Jun-02 16:42 
GeneralRe: GDI+ Pin
Nish Nishant18-Jun-02 18:28
sitebuilderNish Nishant18-Jun-02 18:28 
GeneralRe: GDI+ Pin
Alex Cramer19-Jun-02 17:04
Alex Cramer19-Jun-02 17:04 
GeneralRe: GDI+ Pin
Nish Nishant19-Jun-02 17:17
sitebuilderNish Nishant19-Jun-02 17:17 
GeneralRe: GDI+ Pin
Christian Graus19-Jun-02 17:49
protectorChristian Graus19-Jun-02 17:49 
GeneralRe: GDI+ Pin
Nish Nishant19-Jun-02 18:11
sitebuilderNish Nishant19-Jun-02 18:11 
Christian Graus wrote:
Why - because they steal software ? He does not OWN VS.NET.

I know CG, I know! Oh well, I won't win this argument, so I won't even argue! But I hope you'll understand that the day I earn money nice and proper I'll go fully legal. Right it's not even worth trying! MS won't lose anything in a way since even otherwise I wouldn't be able to afford any of this stuff!

I dunno about Russia though. I kinda fancied that Russians were a rich people!

Nish



Author of the romantic comedy

Summer Love and Some more Cricket [New Win]

GeneralRe: GDI+ Pin
Christian Graus19-Jun-02 18:23
protectorChristian Graus19-Jun-02 18:23 
GeneralRe: GDI+ Pin
Jinhyuck Jung12-Nov-02 21:41
Jinhyuck Jung12-Nov-02 21:41 
GeneralRe: GDI+ Pin
Christian Graus13-Nov-02 0:13
protectorChristian Graus13-Nov-02 0:13 
GeneralRe: GDI+ (please tell me how) Pin
chachoo19-Feb-04 4:14
chachoo19-Feb-04 4:14 
GeneralUsefull... Pin
Jean-Michel LE FOL9-Jun-02 23:22
Jean-Michel LE FOL9-Jun-02 23:22 
GeneralRe: Usefull... Pin
Nish Nishant10-Jun-02 0:57
sitebuilderNish Nishant10-Jun-02 0:57 
GeneralRe: Usefull... Pin
10-Jun-02 4:53
suss10-Jun-02 4:53 
GeneralVery useful to me! Pin
nilaysoft9-Jun-02 20:54
nilaysoft9-Jun-02 20:54 
GeneralRe: Very useful to me! Pin
Nish Nishant9-Jun-02 21:13
sitebuilderNish Nishant9-Jun-02 21:13 

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