In the vanilla code, for the recipe book "ghost" recipe's, AbstractGui.fill is used to draw a gray transparent rectangle over the items which makes it look like they're see-through.

I've been trying to use this trick myself, but I can't seem to figure out how to manipulate the color that function uses. Inside it, the integer get somehow decoded (my knowledge doesn't go far when it comes to what I think is called bit-shifting?)

float f3 = (float)(p_fill_4_ >> 24 & 255) / 255.0F;
float f = (float)(p_fill_4_ >> 16 & 255) / 255.0F;
float f1 = (float)(p_fill_4_ >> 8 & 255) / 255.0F;
float f2 = (float)(p_fill_4_ & 255) / 255.0F;
GlStateManager.color4f(f, f1, f2, f3);

 

Here's how it get called.

AbstractGui.fill(j, k, j + 16, k + 16, 822083583);

 

Does anyone know how I would go at changing the color/transparency of the fill?

Worked like a charm! Too bad none of the hex color pickers seem to have an AARRGGBB option. So I had to get a normal RRGGBB hex code, then convert some arbitrary value (I think it was 201) to hexadecimal which is the C9 value. 

	public void renderGhostItem(ItemStack stack, int x, int y) {
	      RenderHelper.enableGUIStandardItemLighting();
	      GlStateManager.disableLighting();
	      
	      itemRenderer.renderItemAndEffectIntoGUI(stack, x, y);
	      GlStateManager.depthFunc(516);
          AbstractGui.fill(x, y, x + 16, y + 16, 0xC9365A7F);
          GlStateManager.depthFunc(515);
          renderGhostItemOverlay(font, stack, x, y);
          
	      GlStateManager.enableLighting();
	      RenderHelper.disableStandardItemLighting();
	}

This is what it looks like now

 

1 hour ago, Tessa said:

Worked like a charm! Too bad none of the hex color pickers seem to have an AARRGGBB option. So I had to get a normal RRGGBB hex code, then convert some arbitrary value (I think it was 201) to hexadecimal which is the C9 value. 

The AA is just the alpha value (in the range of [0, 255]). You can use 255 (opaque) if you do not want transparency.

3 hours ago, DavidM said:

The AA is just the alpha value (in the range of [0, 255]). You can use 255 (opaque) if you do not want transparency.

Yes! That's right, but you need to convert the 0-255 value to hexadecimal. Because the fill function decodes the number you give it like this.
 

public static void fill(int p_fill_0_, int p_fill_1_, int p_fill_2_, int p_fill_3_, int p_fill_4_) {

      float f3 = (float)(p_fill_4_ >> 24 & 255) / 255.0F;
      float f = (float)(p_fill_4_ >> 16 & 255) / 255.0F;
      float f1 = (float)(p_fill_4_ >> 8 & 255) / 255.0F;
      float f2 = (float)(p_fill_4_ & 255) / 255.0F;

      GlStateManager.color4f(f, f1, f2, f3);
   }