Line broken on specific float values

[zaafar]

Sorry if this question had being asked before, kindly refresh my memory if it is. Why in the following image the line gets broken when I change the box size. (code given below)

private static float X = 0.0f;
private static float Y = 619.500f;
private static float W = 351.0f;
private static float H = 248.0f;

// then in the render function

ImGui.DragFloat("X", ref X);
ImGui.DragFloat("Y", ref Y);
ImGui.DragFloat("W", ref W);
ImGui.DragFloat("H", ref H);
ImGui.GetBackgroundDrawList().AddRect(new Vector2(X, Y), new Vector2(X + W, Y + H), 0xFFFFFFFF);

[zaafar]

@mellinoe any idea?

[Alan-FGR]

Possibly your rasterizer playing tricks. It's definitely not a geometry problem (i.e. the line is not actually broken), it's rendering. I'm not sure how imgui works internally to generate lines but maybe it just creates a 1"px" geometry that your rasterizer fails to detect as pixels, what makes sense especially given the imprecision of the floats gpus deal with. If you want more elaboration do a c/cpp repro and ask in the imgui repo. One possible solution would be to snap to integers in the shader. Possibly that should be done by default I'd say.

[zaafar]

i did it on c++ imgui directly and couldn't reproduce the issue. following is the code i used.

float x = 0.0f;
float y = 619.500f;
float w = 351.0f;
float h = 248.0f;
ImGui::GetBackgroundDrawList()->AddRect(ImVec2(x, y), ImVec2(x + w, y + h), 0xFFFFFFFF, 0.0f, ImDrawFlags_RoundCornersNone);

[zaafar]

figured out the solution, have to use LinearSampler over here (https://github.com/mellinoe/ImGui.NET/blob/master/src/ImGui.NET.SampleProgram/ImGuiController.cs#L133) rather than PointSampler.

thx to Mellinoe and RenderDocs for all the help!

[zaafar]

issue fixed: ocornut/imgui#5156