How to make an image that is transparent in the background?

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Hello friends;

As I have tested before, we can just use images that are bmp type and also they should be 16 and 24 I think. I wanted to make an object that has no background. Let me explain with an example:

I used this article. The problem is when I want to create an image I don't know how to make transparent background. I used black bg and white bg, but none of them worked.
Do you know how I can fix it?

Graphical Interfaces XI: Integrating the Standard Graphics Library (build 16)
Graphical Interfaces XI: Integrating the Standard Graphics Library (build 16)
  • 2017.10.16
  • www.mql5.com
A new version of the graphics library for creating scientific charts (the CGraphic class) has been presented recently. This update of the developed library for creating graphical interfaces will introduce a version with a new control for creating charts. Now it is even easier to visualize data of different types.
 

The reason isn't the black vs white background — it's that a 24-bit BMP has no alpha channel at all, so there's nothing to make transparent. Two things usually fix this:

1. If you don't actually need an image file, skip the BMP and draw straight onto a canvas with an alpha-capable format. The default  CreateBitmapLabel  format is  COLOR_FORMAT_XRGB_NOALPHA  (opaque) — that's the usual culprit. Use  ARGB_NORMALIZE  and erase to a fully transparent background:

#include <Canvas\Canvas.mqh>
CCanvas canvas;
canvas.CreateBitmapLabel("myImg", x, y, w, h, COLOR_FORMAT_ARGB_NORMALIZE);
canvas.Erase(0);                                   // 0 = fully transparent
canvas.FillCircle(w/2, h/2, 40, ColorToARGB(clrDodgerBlue, 255));
canvas.Update();

Erase(0) leaves the background see-through and only what you draw (with alpha in the color's A byte) shows up.

2. If you specifically need to load a picture, it has to be a 32-bit BMP with a real alpha channel — and save it in top-down row order. CCanvas has a long-standing quirk where a bottom-up BMP renders only the top half, which sends a lot of people down the wrong path.

ARGB_NORMALIZE premultiplies alpha for you, so blending over the chart looks correct out of the box. Start there.

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