Add transparency threshold on pushImage() function

[matthieuweber]

Hello,

As a new feature suggestion I tried to modify the pushImage() function to be able to set a transparency threshold.
It works :)

I just changed the line :

if (transp != *ptr)

with :

if (transp < *ptr) // Enable transparent color threshold

Then I defined a global variable : int Transparency_th = 0; // Transparency threshold

(Transparency_th could be a class variable)

Eventually, I defined my custom tft_output like this :

/////////////////////////////////////////////////////////////////////////////////
// bool tft_output(int16_t x, int16_t y, uint16_t w, uint16_t h, uint16_t* bitmap)
// This next function will be called during decoding of the jpeg file to
// render each block to the TFT.  If you use a different TFT library
// you will need to adapt this function to suit.
/////////////////////////////////////////////////////////////////////////////////
bool tft_output(int16_t x, int16_t y, uint16_t w, uint16_t h, uint16_t* bitmap)
{
// Stop further decoding as image is running off bottom of screen
if ( y >= Tft.height() )  return 0;
// This function will clip the image block rendering automatically at the TFT boundaries
//----------
if (Transparency_th> 0)  Tft.pushImage(x, y, w, h, bitmap, Tft.color565(Transparency_th, Transparency_th, Transparency_th));  // With transparency effect for dankest pixels on loaded jpg pictures
//----------
else  Tft.pushImage(x, y, w, h, bitmap);
return 1;  // Return 1 to decode next block
}

Usage :

(This modification doesn't break already made projects.)

      Transparency_th= 50;                     // Darkest pixels (< 50 out of  255) will not be rendered (= transparent) on jpg images   
      TJpgDec.drawFsJpg(158, 75, "My_picture.jpg", LittleFS); 
      Transparency_th= 0;                      // All pixels will be rendered

The modified pushImage function

/***************************************************************************************
** Function name:           pushImage
** Description:             plot 16 bit sprite or image with 1 colour being transparent
***************************************************************************************/
void TFT_eSPI::pushImage(int32_t x, int32_t y, int32_t w, int32_t h, uint16_t *data, uint16_t transp)
{
  PI_CLIP;

  begin_tft_write();
  inTransaction = true;

  data += dx + dy * w;


  uint16_t  lineBuf[dw]; // Use buffer to minimise setWindow call count

  // The little endian transp color must be byte swapped if the image is big endian
  if (!_swapBytes) transp = transp >> 8 | transp << 8;

  while (dh--)
  {
    int32_t len = dw;
    uint16_t* ptr = data;
    int32_t px = x, sx = x;
    bool move = true;
    uint16_t np = 0;

    while (len--)
    {
    //----------  

    //  if (transp != *ptr)      <= Removed line

    if (transp < *ptr)   // New line, to enable transparent color threshold

    //----------
          {
        if (move) { move = false; sx = px; }
        lineBuf[np] = *ptr;
        np++;
      }
      else
      {
        move = true;
        if (np)
        {
          setWindow(sx, y, sx + np - 1, y);
          pushPixels((uint16_t*)lineBuf, np);
          np = 0;
        }
      }
      px++;
      ptr++;
    }
    if (np) { setWindow(sx, y, sx + np - 1, y); pushPixels((uint16_t*)lineBuf, np); }

    y++;
    data += w;
  }

  inTransaction = lockTransaction;
  end_tft_write();
}

[Bodmer]

Can you decribe an example scenario where this is useful.

[matthieuweber]

Sorry for the delay (I didn't checked the link to the discussion forward)

Actually I believe we can do se same with sprites, but this is a very minor code change which do the same goal :
Display a jpg with transparent color :

Imagine you want to add an icon form Internet to your TFT display, the icon is not square (for example; a flame).
On the computer, you paint in black the background, but some edges will stay not totally black, so if you don't set a threshold, some black marks will stay surrounding the flame. So I preferred keep it like this picture :

And as a result :

[matthieuweber]

so you can adjust threshold to have the best rendering... (by the way sorry for the picture quality!)