AlwaysAutoResize window not resized on first call.

[sc00ter]

master branch

Nothing is drawn the first time this is called, unless ImGui::SetNextWindowSize(...) is called prior to Begin().

ImGui::NewFrame();
ImGui::SetNextWindowPos(ImVec2(x, y), ImGuiCond_Always);
ImGui::Begin("", nullptr,  
  ImGuiWindowFlags_NoMove|ImGuiWindowFlags_NoTitleBar
  |ImGuiWindowFlags_NoResize|ImGuiWindowFlags_AlwaysAutoResize
  |ImGuiWindowFlags_NoSavedSettings
  |ImGuiWindowFlags_NoFocusOnAppearing
  |ImGuiWindowFlags_NoNav); 
ImGui::Text("%s", text);
ImGui::End();
ImGui::EndFrame();
ImGui::Render();
auto dd = ImGui::GetDrawData();

assert(dd->TotalVtxCount > 0); // will fail on first run.

Cheers.

[ocornut]

That's intentional, we need to compute the contents size on the first frame so the window can have a size on the next frame.

What's the issue with it?

[sc00ter]

It's not a huge deal, but it is showing up as an error on a vulkan based render test case.
Basically vulkan is recording a command buffer which is using imgui to draw some text overlays.
As the command buffers only get created once upfront, and not for each frame, it will always fail.

[ocornut]

it is showing up as an error on a vulkan based render test case.

If there is an error in the Vulkan example could you clarify what/where the error is?

I can't seem to reproduce any error even when taking this early return path in ImGui_ImplVulkan_RenderDrawData():

void ImGui_ImplVulkan_RenderDrawData(VkCommandBuffer command_buffer, ImDrawData* draw_data)
{
    VkResult err;
    if (draw_data->TotalVtxCount == 0)
        return;

[sc00ter]

Sorry, I don't mean in the Vulkan example in imgui. I'm referring to a vulkan project I am working on.

To clarify, in this particular case, the command buffer is pre-recorded once, but submitted to vulkan's render queue each frame, rather than being re-recorded each frame. So in the case where no window size is given, the above issue occurs.

Perhaps this use case, albeit a common vulkan scenario, is a little outside the scope of imgui's general design.

[ocornut]

I see. Dear ImGui can't give you guarantee that things will appear on the first frame unless you explicitly size them. If you want to hold on a pre-recorded command buffer (which seems a little odd) maybe you can call the imgui NewFrame/Render set twice before turning the ImDrawData structure into a command buffer?

[sc00ter]

sure, thanks for the help.