[SDL] How to gray out a button image?

[Ken Rogoway]

The easiest way is to keep track of the button state and if it is disabled,
you draw a grayed out version of the button.  If you are using C++ you can
write a simple button class to handle tracking the state info, but if you
are using C you can still do the same thing but the data will need to be
stored someplace else.

Below is an example.  This is not meant to be a complete solution, but
rather enough for you to understand the approach I am suggesting:

// Simple C++ button draw.  All vars used are class members.  You can also
// get the values to use in the dstRect directly from the SDL_Surface, but
// that is beyond the scope of this example.
void Button::Draw()
{
    SDL_Rect dstRect;

    dstRect.x = btnX;    // Class member for button X
    dstRect.y = btnY;    // Class member for button Y
    dstRect.w = btnW;    // Class member for button Width
    dstRect.h = btnH;    // Class member for button Height

    switch( btnState )
    {
        case eButtonUp:
        case eButtonDown:
        case eButtonDisabled:
            SDL_BlitSurface( btnImages[btnState],NULL,screen,&dstRect );
            break;

        default:
            assert( false );
    }
}
// Simple C version of button draw.
// Array of button images is passed in along with the state and X, Y
location
// You can also get the values to use in the dstRect directly from the
// SDL_Surface, but that is beyond the scope of this example.

void DrawButton( SDL_Surface *btnImages,int btnX,int btnY,int btnState )
{
    SDL_Rect dstRect; 

    dstRect.x = btnX;
    dstRect.y = btnY;
    dstRect.w = 64;    // Hard coded, you would either pass this in or get
it from the image
    dstRect.h = 32;    // Hard coded, you would either pass this in or get
it from the image

    switch( btnState )
    {
        case eButtonUp:
        case eButtonDown:
        case eButtonDisabled:
            SDL_BlitSurface( btnImages[btnState],NULL,screen,&dstRect );
            break;

        default:
            assert( false );
    }
}

I didn't compile any of this so if there are typos I apologize.  I hope this
helps you.

Ken Rogoway
Homebrew Software
HYPERLINK "http://www.homebrewsoftware.com/"http://www.homebrewsoftware.com/


-----Original Message-----
From: sdl-bounces at lists.libsdl.org [HYPERLINK
"mailto:sdl-bounces at lists.libsdl.org"mailto:sdl-bounces at lists.libsdl.org] On
Behalf Of Erik
Sent: Tuesday, April 08, 2008 6:27 PM
To: A list for developers using the SDL library. (includes SDL-announce)
Subject: [SDL] How to gray out a button image?

We need to gray out[1] buttons with images on in our toolkit. I just wonder
what is the best way to gray out the image. Has anyone done that before?
Does it need SDL_gfx or just SDL?

[1] [HYPERLINK
"http://en.wikipedia.org/wiki/Grayed_out"http://en.wikipedia.org/wiki/Grayed
_out]
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