C-API How to invert the pixels of an LCDBitmap?

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#1

I want to invert the pixels of an LCDBitmap in-situ.

This post says there is a way to get 4bpp pixel data from the bitmap - is this only in Lua?

The only relevant C-API function I can find is:

void playdate->graphics->getBitmapData(LCDBitmap* bitmap, int* width, int* height, int* rowbytes, uint8_t** mask, uint8_t** data);

Which returns:

The data is 1 bit per pixel packed format, in MSB order

So I don't see how I can handle transparent pixels ... maybe these are automatically built into the mask at load-time, but loadBitmap() does not specify.

Thoughts?

#2

Ok, going with this for the moment.
It's a fairly "heavy" approach.

LCDBitmap *duplicateBitmapInverted( LCDBitmap *base )
{
    assert( base );
    LCDBitmap *bitmap_copy;

    int width;
    int height;
    playdate->graphics->getBitmapData( base, &width, &height, NULL, NULL, NULL );

    bitmap_copy = playdate->graphics->newBitmap( width, height, kColorClear );

    if ( bitmap_copy != NULL )
    {
        playdate->graphics->pushContext( bitmap_copy );
        playdate->graphics->setDrawMode( kDrawModeInverted );
        playdate->graphics->drawBitmap( base, 0, 0, kBitmapUnflipped );
        playdate->graphics->setDrawMode( kDrawModeCopy );  // maybe not correct
        playdate->graphics->popContext();
    }

    return bitmap_copy;
}
#4

It might be easier to just flip the bits in the data.

for(int y=0; y < height; y++){
  for(int x=0; x < width/8; x++){
    data[x] = ~data[x];
  }
  data += rowbytes; //advance the pointer a row
}

this code is completely untested and is intended as inspiration.

#5

Looks interesting!

So you're not specifically handling the transparency.
I will give it a test.