ImFont::RenderText() issue

[tksuoran]

Version/Branch of Dear ImGui:

Version: 1.89.3
Branch: docking

Back-end/Renderer/Compiler/OS

Back-ends: custom / erhe
Compiler: VS 2022 17.4.4
Operating System: Windows 10

My Issue/Question:

I encountered IM_ASSERT_PARANOID() failure in ImDrawList::PrimReserve() due to negative arguments being passed from ImFont::RenderText(). This was caused by s pointing to one past text_end. text_begin pointed to Material and text_end looked valid. I am not sure exactly what path resulted in s pointing to text_end + 1. I have not been able to repro, so this may be some corner case that is not easy to hit.

[ocornut]

Intuitively I imagine ccf94e2 could be at fault because it is a very-recent change that align with some of the elements of that issues. If you repro more details would be useful.

Or: was text-wrapping active? that's to rule out whole chunks of code including bits that have changed.

[tksuoran]

I can now repro. This happens with TreeNodeEx() that gets completely clipped / scrolled so that it is not visible, with flags ImGuiTreeNodeFlags_OpenOnArrow | ImGuiTreeNodeFlags_OpenOnDoubleClick |ImGuiTreeNodeFlags_SpanFullWidth, word_wrap_enabled == false.

Perhaps // Fast-forward to first visible line is at fault, when there is no line at all that is visible? That code section has s = line_end + 1.

[tksuoran]

Indeed the code path in my previous comment is executed and that is how s gets text_end + 1 value.

[tksuoran]

+		this	0x000001e03dc44f80 {IndexAdvanceX={Size=256 Capacity=256 Data=0x000001e0313a0bf0 {6.00000000} } FallbackAdvanceX=...}	const ImFont *
+		clip_rect	{x=1.00000000 y=699.000000 z=168.000000 ...}	const ImVec4 &
		col	2634022911	unsigned int
		col_untinted	3435973836	const unsigned int
		cpu_fine_clip	false	bool
+		draw_list	0x000001e0046c8e78 {CmdBuffer={Size=1 Capacity=8 Data=0x000001e01ef86e30 {ClipRect={x=1.00000000 y=699.000000 ...} ...} } ...}	ImDrawList *
		idx_count_max	-6	const int
		idx_expected_size	15	const int
+		idx_write	0xcccccccccccccccc {???}	unsigned short *
		line_height	17.0000000	const float
+		pos	{x=44.0000000 y=681.000000 }	const ImVec2 &
+		s	0x00007ff67604a8b1 ""	const char *
		scale	1.00000000	const float
		size	17.0000000	float
		start_x	44.0000000	const float
+		text_begin	0x00007ff67604a8a8 "Material"	const char *
+		text_end	0x00007ff67604a8b0 ""	const char *
		vtx_count_max	-4	const int
		vtx_index	3435973836	unsigned int
+		vtx_write	0xcccccccccccccccc {pos={x=??? y=??? } uv={x=??? y=??? } col=??? }	ImDrawVert *
		word_wrap_enabled	false	const bool
+		word_wrap_eol	0xcccccccccccccccc <Error reading characters of string.>	const char *
		wrap_width	0.00000000	float
		x	44.0000000	float
		y	698.000000	float

[ocornut]

Thank you, I can repro with #define IMGUI_DEBUG_PARANOID. Now going to lunch but going to look into this afterwards.

[ocornut]

Broken by 3482d4e (#5720, #5919)

[ocornut]

Pushed fix 867bdbe

Interestingly, it would trigger with IMGUI_DEBUG_PARANOID defined, but without it would work as the count is cancelled at the end of the function (but it would run some extra code unnecessarily).

Thank you!