Method AddDrawListToDrawDataEx

imgui_tiny_app/imgui/imgui_draw.cpp:2278–2321

Important: 'out_list' is generally going to be draw_data->CmdLists, but may be another temporary list as long at it is expected that the result will be later merged into draw_data->CmdLists[].

// Important: 'out_list' is generally going to be draw_data->CmdLists, but may be another temporary list
// as long at it is expected that the result will be later merged into draw_data->CmdLists[].
void ImGui::AddDrawListToDrawDataEx(ImDrawData* draw_data, ImVector<ImDrawList*>* out_list, ImDrawList* draw_list)
{
    if (draw_list->CmdBuffer.Size == 0)
        return;
    if (draw_list->CmdBuffer.Size == 1 && draw_list->CmdBuffer[0].ElemCount == 0 && draw_list->CmdBuffer[0].UserCallback == NULL)
        return;

    // Draw list sanity check. Detect mismatch between PrimReserve() calls and incrementing _VtxCurrentIdx, _VtxWritePtr etc.
    // May trigger for you if you are using PrimXXX functions incorrectly.
    IM_ASSERT(draw_list->VtxBuffer.Size == 0 || draw_list->_VtxWritePtr == draw_list->VtxBuffer.Data + draw_list->VtxBuffer.Size);
    IM_ASSERT(draw_list->IdxBuffer.Size == 0 || draw_list->_IdxWritePtr == draw_list->IdxBuffer.Data + draw_list->IdxBuffer.Size);
    if (!(draw_list->Flags & ImDrawListFlags_AllowVtxOffset))
        IM_ASSERT((int)draw_list->_VtxCurrentIdx == draw_list->VtxBuffer.Size);

    // Check that draw_list doesn't use more vertices than indexable (default ImDrawIdx = unsigned short = 2 bytes = 64K vertices per ImDrawList = per window)
    // If this assert triggers because you are drawing lots of stuff manually:
    // - First, make sure you are coarse clipping yourself and not trying to draw many things outside visible bounds.
    //   Be mindful that the lower-level ImDrawList API doesn't filter vertices. Use the Metrics/Debugger window to inspect draw list contents.
    // - If you want large meshes with more than 64K vertices, you can either:
    //   (A) Handle the ImDrawCmd::VtxOffset value in your renderer backend, and set 'io.BackendFlags |= ImGuiBackendFlags_RendererHasVtxOffset'.
    //       Most example backends already support this from 1.71. Pre-1.71 backends won't.
    //       Some graphics API such as GL ES 1/2 don't have a way to offset the starting vertex so it is not supported for them.
    //   (B) Or handle 32-bit indices in your renderer backend, and uncomment '#define ImDrawIdx unsigned int' line in imconfig.h.
    //       Most example backends already support this. For example, the OpenGL example code detect index size at compile-time:
    //         glDrawElements(GL_TRIANGLES, (GLsizei)pcmd->ElemCount, sizeof(ImDrawIdx) == 2 ? GL_UNSIGNED_SHORT : GL_UNSIGNED_INT, idx_buffer_offset);
    //       Your own engine or render API may use different parameters or function calls to specify index sizes.
    //       2 and 4 bytes indices are generally supported by most graphics API.
    // - If for some reason neither of those solutions works for you, a workaround is to call BeginChild()/EndChild() before reaching
    //   the 64K limit to split your draw commands in multiple draw lists.
    if (sizeof(ImDrawIdx) == 2)
        IM_ASSERT(draw_list->_VtxCurrentIdx < (1 << 16) && "Too many vertices in ImDrawList using 16-bit indices. Read comment above");

    // Resolve callback data pointers
    if (draw_list->_CallbacksDataBuf.Size > 0)
        for (ImDrawCmd& cmd : draw_list->CmdBuffer)
            if (cmd.UserCallback != NULL && cmd.UserCallbackDataOffset != -1 && cmd.UserCallbackDataSize > 0)
                cmd.UserCallbackData = draw_list->_CallbacksDataBuf.Data + cmd.UserCallbackDataOffset;

    // Add to output list + records state in ImDrawData
    out_list->push_back(draw_list);
    draw_data->CmdListsCount++;
    draw_data->TotalVtxCount += draw_list->VtxBuffer.Size;
    draw_data->TotalIdxCount += draw_list->IdxBuffer.Size;
}

void ImDrawData::AddDrawList(ImDrawList* draw_list)
{