Drawing a pixel buffer to the screen

[tommitytom]

I have a simple RGBA pixel buffer that I want to render to my UI every frame. My first thought was to create a texture/bitmap, write the pixels to it every frame and call IGraphics.DrawBitmap. However I can't work out how to create a bitmap. After a bit of digging I found that IGraphicsNanoVG.CreateAPIBitmap exists but it is not exposed, and even then the IBitmap and APIBitmap don't seem to offer a way of setting pixel data. Any suggestions on how to do this?

[olilarkin]

have to discuss with @AlexHarker how we do this in a cross -graphics api way. Here is how you can do it with nanovg:

#define IMG_SIZE 300
//https://github.com/memononen/nanovg/issues/269#issuecomment-189381540
void drawImageTest(NVGcontext* vg, float x, float y, float w, float h, float t)
{
  static int img = -1;
  NVGpaint imgPaint;
  int i, j;
  unsigned char data[IMG_SIZE*IMG_SIZE*4];
  
  if (img == -1) {
    unsigned char* px = data;
    for (i = 0; i < IMG_SIZE; i++) {
      for (j = 0; j < IMG_SIZE; j++) {
        unsigned char g = (((i>>1) ^ (j>>1)) & 1) * 255;
        px[0] = 255;
        px[1] = 255;
        px[2] = 255;
        px[3] = g;
        px += 4;
      }
    }
    img = nvgCreateImageRGBA(vg, IMG_SIZE, IMG_SIZE, 0, data);
  } else {
    unsigned char c = (unsigned char)((1+sinf(t))*0.5f*255.0f);
    unsigned char* px = data;
    for (i = 0; i < IMG_SIZE; i++) {
      for (j = 0; j < IMG_SIZE; j++) {
        unsigned char g = (((i>>1) ^ (j>>1)) & 1) * 255;
        px[0] = c;
        px[1] = c;
        px[2] = c;
        px[3] = g;
        px += 4;
      }
    }
    nvgUpdateImage(vg, img, data);
  }
  
  nvgBeginPath(vg);
  
  imgPaint = nvgImagePattern(vg, x, y, w,h, 0, img, 1.0f);
  
  nvgRect(vg, x, y, w, h);
  nvgFillPaint(vg, imgPaint);
  nvgFill(vg);
}

class DrawRGBAControl : public IControl
{
public:
  DrawRGBAControl(IRECT bounds)
  : IControl(bounds)
  {
  }
  
  void Draw(IGraphics& g) override
  {
    NVGcontext* vg = (NVGcontext*) g.GetDrawContext();
    drawImageTest(vg, mRECT.L, mRECT.T, IMG_SIZE, IMG_SIZE, 1);
  }
};

[tommitytom]

Thanks for the code, works a treat! Certainly curious as to a cross platform method, however :)

[AlexHarker]

Your pixel buffer is in memory, correct? I think we could add a loader for pixel buffers, but be good to figure out how that behaviour should work exactly.

[tommitytom]

Yes, I'm generating it each frame. Before I moved to iPlug2 I was just using raw GL - writing the pixels to a texture every frame and drawing it to a quad