[Renderers/IMGUI] Create minimal ImDrawList example

[THISISAGOODNAME]

Inspired by #69

[nicbarker]

This is a super cool idea and I will check it out, but just as a heads up I think we'll likely clone in imgui & sokol rather than include them inside the repo 👍

[nicbarker]

I just had a look at this and unfortunately I can't get it to compile on my mac out of the box, will try again tomorrow 🙂

[THISISAGOODNAME]

@nicbarker Sorry, I forgot to link cocoa and openGL on mac platform. Updated.

[nicbarker]

Hey @THISISAGOODNAME, I just updated to latest and there's something odd going on with clang & cmake on mac. I'm getting errors along the lines of unknown type name 'NSString' from sokol - I suspect it's attempting to import the obj-c headers as C/C++. I'll have another look at this when I have time 🙂

[illusion0001]

Found a few things needed for new api to compile.

• Clay_Arena doesn't have label anymore, so Clay_CreateArenaWithCapacityAndMemory is preferred instead (taken from example).
• measureText callback needed userdata param (I provided 0 here).

Clay_Dimensions measureText(Clay_StringSlice text, Clay_TextElementConfig* config, uintptr_t userData)
{
    ImVec2 size = ImGui::CalcTextSize(text.chars, nullptr);
    return (Clay_Dimensions)
    {
        .width = size.x,
        .height = size.y,
    };
}

void initClay()
{
    uint64_t totalMemorySize = Clay_MinMemorySize();
    Clay_Arena clayMemory = Clay_CreateArenaWithCapacityAndMemory(totalMemorySize, (char*)malloc(totalMemorySize));
    Clay_Initialize(clayMemory, Clay_Dimensions{
        1280, 720 }, Clay_ErrorHandler{ HandleClayErrors });
    Clay_SetMeasureTextFunction(measureText, 0);
    Clay_Initialize(clayMemory, (Clay_Dimensions)
    {
        1280, 720
    }, { errorCallback, 0 });
}

Optionally, you can use GetForegroundDrawList to avoid imgui creating a window for it. (p should be 0 so it starts at top left!

void render(Clay_RenderCommandArray renderCommands)
{
    ImDrawList* draw_list = ImGui::GetForegroundDrawList();
    // start from 0,0
    static ImVec2 p = {};
    //...
}

[illusion0001]

Here is demo document rendered using this PR and adjustments from this file https://github.com/KosmosisDire/VoxyEnginePlus/blob/8665459f1c394a299e6144af4e9e180f9faebcb7/app-framework/src/clayui/elements/helper/clay-imgui-renderer.hpp
for mouse, you may use ImGui IO for it.

    ImGuiIO& io = ImGui::GetIO();
    ImVec2 mousePosition = io.MousePos;
    ImVec2 scrollDelta = { io.MouseWheel ,io.MouseWheel };