When using ImGui.GetWindowDrawList(), nothing is rendered

[odalet]

I'm trying to port over to C# ocornut's 'ImDrawList' test bench (see here: ocornut/imgui#3606).

I'm retrieving the window draw list with ImGui.GetWindowDrawList() and then using primitives on the resulting draw list. However, I can't seem to get results displayed.

Here is the code I'm using based on ImGui.NET.SampleProgram: I replaced SubmitUI but the rest of the code is the same:

private static unsafe void SubmitUI()    
{
    // See (https://gist.github.com/ocornut/51367cc7dfd2c41d607bb0acfa6caf66)
    _ = ImGui.Begin("FX", ImGuiWindowFlags.AlwaysAutoResize);
    ImGui.Text("BEFORE");

    var size = new Vector2(320f, 180f);
    _ = ImGui.InvisibleButton("canvas", size);
    var p0 = ImGui.GetItemRectMin();
    var p1 = ImGui.GetItemRectMax();

    var drawList = ImGui.GetWindowDrawList();
    drawList.PushClipRect(p0, p1);

    var io = ImGui.GetIO();
    var mouseData = new Vector4
    {
        X = (io.MousePos.X - p0.X) / size.X,
        Y = (io.MousePos.Y - p0.Y) / size.Y,
        Z = io.MouseDownDuration[0],
        W = io.MouseDownDuration[1]
    };

    //drawList.AddRectFilled(p0, p1, MakeColor32(255, 0, 0, 255));
    Fx(drawList, p0, p1, size, mouseData, (float)ImGui.GetTime());

    drawList.PopClipRect();

    ImGui.Text("AFTER");
    ImGui.End();
}

private static void Fx(ImDrawListPtr d, Vector2 a, Vector2 b, Vector2 sz, Vector4 mouse, float t)
{
    for (var n = 0; n < (1.0f + Math.Sin(t * 5.7f)) * 40.0f; n++) d.AddCircle(
        new Vector2(a.X + sz.X * 0.5f, a.Y + sz.Y * 0.5f),
        sz.Y * (0.01f + n * 0.03f), MakeColor32(255, (byte)(140 - n * 4), (byte)(n * 3), 255));
}

private static uint MakeColor32(int r, int g, int b, int a) => (uint)((byte)a << 24 & (byte)b << 16 & (byte)g << 8 & (byte)r);

All that I obtain is an empty placeholder:

Any idea why this does not work?

Thanks!

[zaafar]

@odalet

Your color function is wrong, I use the following one.

public static uint Color(byte r, byte g, byte b, byte a) { uint ret = a; ret <<= 8; ret += b; ret <<= 8; ret += g; ret <<= 8; ret += r; return ret; }

OR just update your color function to following

(uint)((byte)a << 24 | (byte)b << 16 | (byte)g << 8 | (byte)r);

[odalet]

@zaafar Thank you... By examining your implementation and comparing it with mine, I saw that all my & should be replaced by | then I saw your second suggestion: that is exactly what I ended up with!

I feel ashamed for having got mixed up between AND and OR... no wonder my code didn't work, I was drawing everything with a transparent color :(
Thanks again!