Method Merge

ImGUI GLFW Tutorial/imgui/imgui_draw.cpp:1705–1774

}

void ImDrawListSplitter::Merge(ImDrawList* draw_list)
{
    // Note that we never use or rely on _Channels.Size because it is merely a buffer that we never shrink back to 0 to keep all sub-buffers ready for use.
    if (_Count <= 1)
        return;

    SetCurrentChannel(draw_list, 0);
    draw_list->_PopUnusedDrawCmd();

    // Calculate our final buffer sizes. Also fix the incorrect IdxOffset values in each command.
    int new_cmd_buffer_count = 0;
    int new_idx_buffer_count = 0;
    ImDrawCmd* last_cmd = (_Count > 0 && draw_list->CmdBuffer.Size > 0) ? &draw_list->CmdBuffer.back() : NULL;
    int idx_offset = last_cmd ? last_cmd->IdxOffset + last_cmd->ElemCount : 0;
    for (int i = 1; i < _Count; i++)
    {
        ImDrawChannel& ch = _Channels[i];

        // Equivalent of PopUnusedDrawCmd() for this channel's cmdbuffer and except we don't need to test for UserCallback.
        if (ch._CmdBuffer.Size > 0 && ch._CmdBuffer.back().ElemCount == 0)
            ch._CmdBuffer.pop_back();

        if (ch._CmdBuffer.Size > 0 && last_cmd != NULL)
        {
            ImDrawCmd* next_cmd = &ch._CmdBuffer[0];
            if (ImDrawCmd_HeaderCompare(last_cmd, next_cmd) == 0 && last_cmd->UserCallback == NULL && next_cmd->UserCallback == NULL)
            {
                // Merge previous channel last draw command with current channel first draw command if matching.
                last_cmd->ElemCount += next_cmd->ElemCount;
                idx_offset += next_cmd->ElemCount;
                ch._CmdBuffer.erase(ch._CmdBuffer.Data); // FIXME-OPT: Improve for multiple merges.
            }
        }
        if (ch._CmdBuffer.Size > 0)
            last_cmd = &ch._CmdBuffer.back();
        new_cmd_buffer_count += ch._CmdBuffer.Size;
        new_idx_buffer_count += ch._IdxBuffer.Size;
        for (int cmd_n = 0; cmd_n < ch._CmdBuffer.Size; cmd_n++)
        {
            ch._CmdBuffer.Data[cmd_n].IdxOffset = idx_offset;
            idx_offset += ch._CmdBuffer.Data[cmd_n].ElemCount;
        }
    }
    draw_list->CmdBuffer.resize(draw_list->CmdBuffer.Size + new_cmd_buffer_count);
    draw_list->IdxBuffer.resize(draw_list->IdxBuffer.Size + new_idx_buffer_count);

    // Write commands and indices in order (they are fairly small structures, we don't copy vertices only indices)
    ImDrawCmd* cmd_write = draw_list->CmdBuffer.Data + draw_list->CmdBuffer.Size - new_cmd_buffer_count;
    ImDrawIdx* idx_write = draw_list->IdxBuffer.Data + draw_list->IdxBuffer.Size - new_idx_buffer_count;
    for (int i = 1; i < _Count; i++)
    {
        ImDrawChannel& ch = _Channels[i];
        if (int sz = ch._CmdBuffer.Size) { memcpy(cmd_write, ch._CmdBuffer.Data, sz * sizeof(ImDrawCmd)); cmd_write += sz; }
        if (int sz = ch._IdxBuffer.Size) { memcpy(idx_write, ch._IdxBuffer.Data, sz * sizeof(ImDrawIdx)); idx_write += sz; }
    }
    draw_list->_IdxWritePtr = idx_write;

    // Ensure there's always a non-callback draw command trailing the command-buffer