Plot: plot a flat line if scale_min==scale_max (#1621)

imgui.cpp

@@ -9287,11 +9287,12 @@ void ImGui::PlotEx(ImGuiPlotType plot_type, const char* label, float (*values_ge
         }
 
         const float t_step = 1.0f / (float)res_w;
+        const float inv_scale = (scale_min == scale_max) ? 0.0f : (1.0f / (scale_max - scale_min));
 
         float v0 = values_getter(data, (0 + values_offset) % values_count);
         float t0 = 0.0f;
-        ImVec2 tp0 = ImVec2( t0, 1.0f - ImSaturate((v0 - scale_min) / (scale_max - scale_min)) );                       // Point in the normalized space of our target rectangle
-        float histogram_zero_line_t = (scale_min * scale_max < 0.0f) ? (-scale_min / (scale_max - scale_min)) : (scale_min < 0.0f ? 0.0f : 1.0f);   // Where does the zero line stands
+        ImVec2 tp0 = ImVec2( t0, 1.0f - ImSaturate((v0 - scale_min) * inv_scale) );                       // Point in the normalized space of our target rectangle
+        float histogram_zero_line_t = (scale_min * scale_max < 0.0f) ? (-scale_min * inv_scale) : (scale_min < 0.0f ? 0.0f : 1.0f);   // Where does the zero line stands
 
         const ImU32 col_base = GetColorU32((plot_type == ImGuiPlotType_Lines) ? ImGuiCol_PlotLines : ImGuiCol_PlotHistogram);
         const ImU32 col_hovered = GetColorU32((plot_type == ImGuiPlotType_Lines) ? ImGuiCol_PlotLinesHovered : ImGuiCol_PlotHistogramHovered);
@@ -9302,7 +9303,7 @@ void ImGui::PlotEx(ImGuiPlotType plot_type, const char* label, float (*values_ge
             const int v1_idx = (int)(t0 * item_count + 0.5f);
             IM_ASSERT(v1_idx >= 0 && v1_idx < values_count);
             const float v1 = values_getter(data, (v1_idx + values_offset + 1) % values_count);
-            const ImVec2 tp1 = ImVec2( t1, 1.0f - ImSaturate((v1 - scale_min) / (scale_max - scale_min)) );
+            const ImVec2 tp1 = ImVec2( t1, 1.0f - ImSaturate((v1 - scale_min) * inv_scale) );
 
             // NB: Draw calls are merged together by the DrawList system. Still, we should render our batch are lower level to save a bit of CPU.
             ImVec2 pos0 = ImLerp(inner_bb.Min, inner_bb.Max, tp0);