Ripple effect Clipping/Overdrawing/Adavced poly to avoid overdraw.

[Gringoniceguy]

Version/Branch of Dear ImGui:

Version: Current
Branch: master

Back-end/Renderer/Compiler/OS

Back-ends: imgui_impl_directx9.cpp + imgui_impl_win32.cpp (or specify if using a custom engine/back-end)
Compiler: msvc (if the question is related to building or platform specific features)
Operating System: window 10

My Issue/Question:

Hello, i am trying to create a ripple effect in Dear ImGui.
Now the issue is that i cannot avoid the circle drawing over the corners of the rounded rect, i have solved this using the inverted rect method mention here.
The issue with this is that it does not anti-alias, it does not do this due to it cutting off all alpha is there a alternative to this?
I cannot see how this problem can be solved with out allowing the circle to also fill that area, i do thought have a few suggestions for a alternative/fix

1. Circle and rounded clipping, you said that this was not going to happen so mostly likely not viable.
2. Some how make the anti-alias run after the overdraw.
3. Instead of using a circle we can use a polygon and only allow it to fill the rect, i think this is super hard as it would require some advanced math.

Is any of this a good idea or should i go back to the drawing board?

Screenshots/Video

This is the thing i want todo

Standalone, minimal, complete and verifiable example: (see #2261)

Dont really see how this fits, would have made it a discussion as it is not really a issue.

EDIT:
Not very good example in reality i wont be using a border else i could just draw it above.

[ocornut]

I don't have an easy answer to this, when you involve transparency and rounded shapes things tend to become tricky.

Answer (3) seemingly is the right solution. Actually @ShironekoBen did implement arbitrary clipping as part of the experimental shadow branch (#1329). It does work but it is rather complicated code and that complexity was one of the reason I was hesitant to merge it (the other and main reason being remaining backend work which is also in the work, see #3761, when that's done we will come back to the shadow stuff).

Your request is interesting because it shows a different use of that clipping function and as thus gives us another reason to merge that clipping code.

See AddSubtractedRect(), ClipPolygonShape(), AddSubtractedRect() functions in imgui_draw.cpp
https:/ocornut/imgui/compare/features/shadows#diff-cae83989d4c25e9856fcccd946a85f9276f60655964430213b41230401931c8a

[Gringoniceguy]

Hello, sorry for the late response i was focusing on some other parts of the project.
I was not able to make this work, this might be due to me not really being that advanced in math.
As i have understood it the function AddSubtractedRect() subtracts a path from a rectangle, so much like drawing a inverse rounded rectangle.
I cant see how this wound not be affected by antialiasing either.

I was not able to make this work and just got really weird results, this is what i got

this is with pathing a full circle.

I don't believe i know enough to attempt to write my own function building on ClipPolygonShape(), so i am stuck here.

Is there something i seriously misunderstood or is it something else.
EDIT: I found out that the rect needs to be twice the y for some reason now it draws the full circle, yet with still the same issue.

[givemesomecake]

I visited the link you shared and found the shared function, but it was not very good and it was not doing my job well enough so I was able to make it what I wanted by doing a few changes on this function and I wanted to share it with you.

void ImDrawList::AddInvertedRectFilled(const ImVec2& p_min, const ImVec2& p_max, ImU32 col, float rounding, ImDrawCornerFlags rounding_corners)
{
    if ((col & IM_COL32_A_MASK) == 0)
        return;
    if (rounding > 0.0f)
        PathInvertedRect(p_min, p_max, col, rounding, rounding_corners);
}

void ImDrawList::PathInvertedRect(const ImVec2& a, const ImVec2& b, ImU32 col, float rounding, ImDrawCornerFlags rounding_corners)
{
    rounding = ImMin(rounding, ImFabs(b.x - a.x) * (((rounding_corners & ImDrawCornerFlags_Top) == ImDrawCornerFlags_Top) || ((rounding_corners & ImDrawCornerFlags_Bot) == ImDrawCornerFlags_Bot) ? 0.5f : 1.0f) - 1.0f);
    rounding = ImMin(rounding, ImFabs(b.y - a.y) * (((rounding_corners & ImDrawCornerFlags_Left) == ImDrawCornerFlags_Left) || ((rounding_corners & ImDrawCornerFlags_Right) == ImDrawCornerFlags_Right) ? 0.5f : 1.0f) - 1.0f);

    if (rounding <= 0.0f || rounding_corners == 0)
        return;
    else
    {
        const float rounding_tl = (rounding_corners & ImDrawCornerFlags_TopLeft) ? rounding : 0.0f;
        const float rounding_tr = (rounding_corners & ImDrawCornerFlags_TopRight) ? rounding : 0.0f;
        const float rounding_br = (rounding_corners & ImDrawCornerFlags_BotRight) ? rounding : 0.0f;
        const float rounding_bl = (rounding_corners & ImDrawCornerFlags_BotLeft) ? rounding : 0.0f;
        PathLineTo(a);
        PathArcTo(ImVec2(a.x + rounding_tl, a.y + rounding_tl), rounding_tl, -3.0, -1.5);
        PathFillConvex(col);

        PathLineTo(ImVec2(b.x, a.y));
        PathArcTo(ImVec2(b.x - rounding_tr, a.y + rounding_tr), rounding_tr, -1.5, -0.205);
        PathFillConvex(col);

        PathLineTo(ImVec2(b.x, b.y));
        PathArcTo(ImVec2(b.x - rounding_br, b.y - rounding_br), rounding_br, 1.5, 0.205);
        PathFillConvex(col);

        PathLineTo(ImVec2(a.x, b.y));
        PathArcTo(ImVec2(a.x + rounding_bl, b.y - rounding_bl), rounding_bl, 3.0, 1.5);
        PathFillConvex(col);
    }
}

The float values ​​I use here are not completely perfect, but they draw more efficiently than the shared PathArcToFast function. I leave a visual of the results below

[Gringoniceguy]

I dont know how you even managed to make this run, as it trigger a assert due to a_min being bigger than a_max. Anyways it still does not address the anti alias issue and only helps rounding(on the shadows branch as master already has good rounding with the new PathArcToFast).

[ocornut]

I dont know how you even managed to make this run, as it trigger a assert due to a_min being bigger than a_max.

See #4030

[Gringoniceguy]

Oops, sadly still does not fix anti-aliasing not working only makes the rounding better on the old version[Of Dear ImGui] as the new version[Of Dear ImGui] looks just fine.