[SDL] How to gray out a button image?

[Ken Rogoway]

Doh!  I over complicated the problem by not fully reading your original
post.  The code posted by the other contributors will help you
programmatically generate a grayed out button.  Caution, doing this realtime
(in your game loop) is slow, so you probably want to create these in your
startup code where you load your image.
 
Ken Rogoway
Homebrew Software
HYPERLINK "http://www.homebrewsoftware.com/"http://www.homebrewsoftware.com/
 
 

   _____  

From: sdl-bounces at lists.libsdl.org [mailto:sdl-bounces at lists.libsdl.org] On
Behalf Of Ken Rogoway
Sent: Tuesday, April 08, 2008 7:42 PM
To: 'A list for developers using the SDL library. (includes SDL-announce)'
Subject: Re: [SDL] How to gray out a button image?





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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