Blit 16-bit RGBX and 2-bit gray scale pixel data

SDL Development
1

I am developing an emulator that simulates different machines. There are 3 types of pixel formats used by these machines:

  • 32-bit 8bpp big endian BGRA
  • 16-bit 4bpp big endian RGBX
  • 2-bit packed gray scale (white, light grey, dark grey, black), 4 pixels per byte

I am blitting the VRAM contents of the 32-bit capable machines using this function (SDL2):

void Screen_Blit32(uint8_t* vram, SDL_Texture* tex) {
	void* src;
	void* dst;
	int src_pitch, dst_pitch;
	uint32_t src_format, dst_format;

	src        = &vram[0];
	src_pitch  = (SCREEN_WIDTH + 32) * 4;
	src_format = SDL_PIXELFORMAT_BGRA32;

	SDL_QueryTexture(tex, &dst_format, NULL, NULL, NULL);
	SDL_LockTexture(tex, NULL, &dst, &dst_pitch);
	SDL_ConvertPixels(SCREEN_WIDTH, SCREEN_HEIGHT, src_format, src, src_pitch, dst_format, dst, dst_pitch);
	SDL_UnlockTexture(tex);
}

or this function (SDL3):

void Screen_Blit32(uint8_t* vram, SDL_Texture* tex) {
	void* src;
	void* dst;
	int src_pitch, dst_pitch;
	SDL_PixelFormat src_format, dst_format;

	src = &vram[0];
	src_pitch  = (SCREEN_WIDTH + 32) * 4;
	src_format = SDL_PIXELFORMAT_BGRA32;

	dst_format = tex->format;
	SDL_LockTexture(tex, NULL, &dst, &dst_pitch);
	SDL_ConvertPixels(SCREEN_WIDTH, SCREEN_HEIGHT, src_format, src, src_pitch, dst_format, dst, dst_pitch);
	SDL_UnlockTexture(tex);
}

Can anyone help with adapting this function for the 16-bit and 2-bit pixel data?