Fixed auto-resize collapse bug introduced by d9a84de

[luney112]

Hi,

This PR addresses the re-introduction of the bug described in #176 caused by d9a84de.

The fix: Only use the SizeContents value if it's collapsed and the auto-resize flag is NOT set. Otherwise, it will not calculate the content size properly.

[ocornut]

I think there is a more general issue here that is unrelated to Auto-resizing window.
This for example leads to a MinSize window:

ImGui::SetNextWindowCollapsed(true, ImGuiCond_Once);
ImGui::Begin("Issue 2336", NULL, ImGuiWindowFlags_NoSavedSettings);
ImGui::Text("This is some text");
ImGui::Text("This is some more text");
ImGui::Text("This is some more text again");
ImGui::End();

So your PR wouldn't address the general case.
(Looking into it)

[ocornut]

Should be fixed now, both for auto-resizing and non-auto-resizing window.
Thanks for the head up and finding this!

Added a test for it.

// Test that a window starting collapsed performs width/contents size measurement on its first few frames.
t = REGISTER_TEST("window", "window_size_collapsed_1");
t->GuiFunc = [](ImGuiTestContext* ctx)
{
    ImGui::SetNextWindowCollapsed(true, ImGuiCond_Once);
    ImGui::Begin("Issue 2336", NULL, ImGuiWindowFlags_NoSavedSettings);
    ImGui::Text("This is some text");
    ImGui::Text("This is some more text");
    ImGui::Text("This is some more text again");

    float w = ImGui::GetWindowWidth();
    if (ctx->FrameCount == 0) // We are past the warm-up frames already
    {
        float expected_w = ImGui::CalcTextSize("This is some more text again").x + ImGui::GetStyle().WindowPadding.x * 2.0f;
        IM_CHECK(ImFabs(w - expected_w) < 1.0f);
    }

    ImGui::End();
};`

[luney112]

Sweet, thanks for taking a look (and the fix!)