Display a bitmap with the DrawTile function...

[FredM67]

I've a bitmap of 72x64, which I can display without problem in "buffer mode".
Since this method needs too much ram, I wanted to draw this bitmap with the drawTile function.
I've tried to cut the bitmap in any possible way, I just get "garbage" on the display.
Here's the code:

const unsigned char logo_bmp[] PROGMEM = {/*DATA*/};
constexpr uint8_t TILE_WIDTH{8};
constexpr uint8_t TILE_HEIGHT{8};
void drawTile(U8X8_SSD1306_128X64_NONAME_HW_I2C &u8x8, const uint8_t *bitmap, uint8_t tileX, uint8_t tileY)
{
  uint8_t tile[TILE_HEIGHT];
  for (uint8_t i = 0; i < TILE_HEIGHT; i++)
  {
   tile[i] = pgm_read_byte(bitmap + (tileY * TILE_HEIGHT + i) * (72 / 8) + tileX);
  }
  u8x8.drawTile(tileX, tileY, 1, tile);
}

and then in setup:

  // Loop through the bitmap and draw each tile
  for (uint8_t y = 0; y < (64 / TILE_HEIGHT); y++)
  {
    for (uint8_t x = 0; x < (72 / TILE_WIDTH); x++)
    {
      drawTile(u8x8, logo_bmp, x, y);
    }
  }

Could someone tell me what I'm doing wrong ?
Or is it simply impossible to do that ?!?
Or is the drawTile method broken ?

Thx
Fred

[olikraus]

I think you need a bitlevel converion of the 8x8 bitmatrix.
A tile (usually) is a bit matrix which looks like this: https://github.com/olikraus/u8g2/wiki/u8x8reference#drawtile

Whereas a BMP has a mirrored bit structure:
byte 0: bit 7, bit 6, bit 5..., bit 0
byte 1: bit 7, bit 6, ...

ok I even dont know if the the BMP starts with MSB or LSB... needs to be figured out...

[FredM67]

Well, I've read all your doc. I used the tool https://javl.github.io/[image2cpp](https://javl.github.io/image2cpp/)/ and tried a lot of combination, including "Swap bits in byte" with the remarks "Useful when working with the u8g2 library."... But somehow, I couldn't find a working solution :-(

[olikraus]

I think that online tool is not able to swap the bytes...

[olikraus]

I have created an example:

u8g2/sys/sdl/u8x8_xbm/main.c

Lines 27 to 67 in b88a767

	uint8_t *get_tile_from_xbm(uint8_t tx, uint8_t ty, uint8_t xbm_byte_width, const unsigned char *xbm)
	{
	static uint8_t d[8];
	uint8_t mask = 1;
	uint8_t i;
	const uint8_t *p = xbm;
	p += tx;
	p += xbm_byte_width*ty*8;
	for( i = 0; i < 8; i++ )
	d[i] = 0;
	for( i = 0; i < 8; i++ )
	{
	if ( *p & 1 ) d[0] |= mask;
	if ( *p & 2 ) d[1] |= mask;
	if ( *p & 4 ) d[2] |= mask;
	if ( *p & 8 ) d[3] |= mask;
	if ( *p & 16 ) d[4] |= mask;
	if ( *p & 32 ) d[5] |= mask;
	if ( *p & 64 ) d[6] |= mask;
	if ( *p & 128 ) d[7] |= mask;
	mask <<= 1;
	p += xbm_byte_width;
	}
	return d;
	}
	void u8x8_draw_xbm(uint8_t tx, uint8_t ty, uint8_t xbm_width, uint8_t xbm_height, const unsigned char *xbm)
	{
	uint8_t x, y;
	uint8_t *tile;
	for( y = 0; y < xbm_height/8; y++ )
	{
	for( x = 0; x < xbm_width/8; x++ )
	{
	tile = get_tile_from_xbm(x, y, xbm_width/8, xbm);
	u8x8_DrawTile(&u8x8, tx+x, ty+y, 1, tile);
	// u8x8.drawTile(tx+x, ty+y, 1, tile);
	}
	}
	}

You probably want to use line 64 instead of line 63.
Moreover this procedure works for XBM, so best is to take your image and save the image as .xbm with "gimp" tool.
Limitation:

• not speed optimized
• image width and height must be multiple of 8

[FredM67]

Thx a lot, I'll try it out tomorrow.

[olikraus]

I have created a complete Arduino example, which also puts the image into PROGMEM area: https://github.com/olikraus/u8g2/blob/b88a767cdfff3fc5c5029ba8b5b2b1470ef60400/sys/arduino/u8x8/DrawXBM/DrawXBM.ino

[FredM67]

A huge thank you for your help, the new example...
I works like a charm ;-)