OpenEuphoria

Re: Palette Problem

• Posted by David Cuny <dcuny at LANSET.COM> May 13, 1999
• 591 views

Gwenakl Joret wrote:

>I've a little problem using palette in Eu using Read_bitmpap() : How
>to Change a palette of a Bmp ? :

The routine readBitmapFromFile() returns the bitmap portion (or an error
code) of the requested bitmap. It reads the requested bitmap, then maps the
bitmap's palette to the current palette. Finally, it replaces the references
in the bitmap from it's original pal to the current pal.

Some obvious points:

1. You need to set the graphics_mode before calling the function.
2. Resolutions with more colors take longer to convert
3. It works in all graphics modes, but higher modes have more colors, so map
better

To speed things up, I can suggest the following:

1. Pete has an assembly version of this on his home page - runs faster!
2. Reduce the colors in the bitmap you are reading, if you can.
3. If you always use the same bitmaps, map them all to the same palette:
    - read all the bitmaps mapped to the same palette
    - save the bitmaps with the new palette
   Once they are converted over, you can use the regular Euphoria tools
again.

Hope this helps!

-- David Cuny

include image.e

procedure abortErr( sequence msg, sequence args )
    -- display an error message and abort
    printf( 1, msg, args )
    abort( 0 )
end procedure

function abs( atom a )
    -- return absolute value
    if a > 0 then
        return a
    else
        return -a
    end if
end function

function convertToPalette( sequence sourcePal )
    -- convert the color list to palette indexes

    atom err, diff, best
    sequence destPal, colorIndex

    -- get palette
    destPal = get_all_palette()

    -- adjust source
    sourcePal = floor( sourcePal/4 )
    -- build holder for results
    colorIndex = repeat( 0, length( sourcePal ) )
    -- look at each entry
    for i = 1 to length( sourcePal ) do

        -- set the last best match as impossibly bad
        best = #FFFFFF

        -- look through the palette
        for entry = 1 to length( destPal ) do

            -- error amount for this entry
            err = 0
            -- for each {rgb}
            for rgb = 1 to 3 do
                -- error is difference between the two
                diff = abs( sourcePal[i][rgb] - destPal[entry][rgb] )
                err = err + diff
            end for
            -- better match than prior best match?
            if err < best then
                -- save error amount
                best = err
                -- store the palette index
                colorIndex[i] = entry
            end if
        end for

    end for
    return colorIndex

end function

function readBitmapFromFile( sequence fName )
    -- load a bitmap from the current file, and map to current palette
    integer index
    sequence replace
    object res

    -- attempt to read bitmap
    res = read_bitmap( fName )
    if integer( res ) then
        -- return the error message
        return res
    end if

    -- adjust the current palette
    replace = convertToPalette(res[1])

    -- replace values with references to new palette
    for i = 1 to length( res[2] ) do
        for j = 1 to length( res[2][i] ) do
            -- get index
            index = res[2][i][j]
            -- get actual color
            index = replace[index+1]-1
            -- replace
            res[2][i][j] = index
        end for
    end for

    -- return bitmap
    return res[2]

end function