ColorEdit: Fix multiple issues. (#4014)

* Change g.ColorEditLastColor type to ImU32 and store RGB color value.
  - Fixes inability to change hue when saturation is 0. (#4014)
  - Fixes edgecases where lossy color conversion prevent restoration of hue/saturation.
  - Fixes hue value jitter when modifying color using SV square.
* Fix hue resetting to 0 when it is set to 255 by explicitly restoring hue if it is 0 and previous value was 1.
* Further reduce hue jitter by restoring hue when color is modified using SV square.

docs/CHANGELOG.txt

@@ -63,6 +63,10 @@ Other Changes:
   The only situation where that change would make a meaningful difference is TreePush((const char*)NULL)
   (_explicitely_ casting a null pointer to const char*), which is unlikely and will now crash.
   You may replace it with anything else.
+- ColorEdit4: Fixed not being able to change hue when saturation is 0. (#4014) [@rokups]
+- ColorEdit4: Fixed hue resetting to 0 when it is set to 255. [@rokups]
+- ColorEdit4: Fixed hue value jitter when source color is stored as RGB in 32-bit integer and perform
+  RGB<>HSV round trips every frames. [@rokups]
 - Menus: Fixed vertical alignments of MenuItem() calls within a menu bar. (broken in 1.84). (#4538)
 - Menus: Adjust closing logic to accomodate for varying font size and dpi.
 - Menus: Fixed crash when navigating left inside a child window inside a sub-menu. (#4510).

imgui.h

@@ -64,7 +64,7 @@ Index of this file:
 // Version
 // (Integer encoded as XYYZZ for use in #if preprocessor conditionals. Work in progress versions typically starts at XYY99 then bounce up to XYY00, XYY01 etc. when release tagging happens)
 #define IMGUI_VERSION               "1.85 WIP"
-#define IMGUI_VERSION_NUM           18416
+#define IMGUI_VERSION_NUM           18417
 #define IMGUI_CHECKVERSION()        ImGui::DebugCheckVersionAndDataLayout(IMGUI_VERSION, sizeof(ImGuiIO), sizeof(ImGuiStyle), sizeof(ImVec2), sizeof(ImVec4), sizeof(ImDrawVert), sizeof(ImDrawIdx))
 #define IMGUI_HAS_TABLE
 

imgui_internal.h

@@ -1606,9 +1606,9 @@ struct ImGuiContext
     ImFont                  InputTextPasswordFont;
     ImGuiID                 TempInputId;                        // Temporary text input when CTRL+clicking on a slider, etc.
     ImGuiColorEditFlags     ColorEditOptions;                   // Store user options for color edit widgets
-    float                   ColorEditLastHue;                   // Backup of last Hue associated to LastColor[3], so we can restore Hue in lossy RGB<>HSV round trips
+    float                   ColorEditLastHue;                   // Backup of last Hue associated to LastColor, so we can restore Hue in lossy RGB<>HSV round trips
-    float                   ColorEditLastSat;                   // Backup of last Saturation associated to LastColor[3], so we can restore Saturation in lossy RGB<>HSV round trips
+    float                   ColorEditLastSat;                   // Backup of last Saturation associated to LastColor, so we can restore Saturation in lossy RGB<>HSV round trips
-    float                   ColorEditLastColor[3];
+    ImU32                   ColorEditLastColor;                 // RGB value with alpha set to 0.
     ImVec4                  ColorPickerRef;                     // Initial/reference color at the time of opening the color picker.
     ImGuiComboPreviewData   ComboPreviewData;
     float                   SliderCurrentAccum;                 // Accumulated slider delta when using navigation controls.
@@ -1777,7 +1777,7 @@ struct ImGuiContext
         TempInputId = 0;
         ColorEditOptions = ImGuiColorEditFlags_DefaultOptions_;
         ColorEditLastHue = ColorEditLastSat = 0.0f;
-        ColorEditLastColor[0] = ColorEditLastColor[1] = ColorEditLastColor[2] = FLT_MAX;
+        ColorEditLastColor = 0;
         SliderCurrentAccum = 0.0f;
         SliderCurrentAccumDirty = false;
         DragCurrentAccumDirty = false;

imgui_widgets.cpp

@@ -4781,6 +4781,30 @@ bool ImGui::ColorEdit3(const char* label, float col[3], ImGuiColorEditFlags flag
     return ColorEdit4(label, col, flags | ImGuiColorEditFlags_NoAlpha);
 }
 
+// ColorEdit supports RGB and HSV inputs. In case of RGB input resulting color may have undefined hue and/or saturation.
+// Since widget displays both RGB and HSV values we must preserve hue and saturation to prevent these values resetting.
+static void ColorEditRestoreHS(const float* col, float* H, float* S, float* V)
+{
+    // This check is optional. Suppose we have two color widgets side by side, both widgets display different colors, but both colors have hue and/or saturation undefined.
+    // With color check: hue/saturation is preserved in one widget. Editing color in one widget would reset hue/saturation in another one.
+    // Without color check: common hue/saturation would be displayed in all widgets that have hue/saturation undefined.
+    // g.ColorEditLastColor is stored as ImU32 RGB value: this essentially gives us color equality check with reduced precision.
+    // Tiny external color changes would not be detected and this check would still pass. This is OK, since we only restore hue/saturation _only_ if they are undefined,
+    // therefore this change flipping hue/saturation from undefined to a very tiny value would still be represented in color picker.
+    ImGuiContext& g = *GImGui;
+    if (g.ColorEditLastColor != ImGui::ColorConvertFloat4ToU32(ImVec4(col[0], col[1], col[2], 0)))
+        return;
+
+    // When S == 0, H is undefined.
+    // When H == 1 it wraps around to 0.
+    if (*S == 0.0f || (*H == 0.0f && g.ColorEditLastHue == 1))
+        *H = g.ColorEditLastHue;
+
+    // When V == 0, S is undefined.
+    if (*V == 0.0f)
+        *S = g.ColorEditLastSat;
+}
+
 // Edit colors components (each component in 0.0f..1.0f range).
 // See enum ImGuiColorEditFlags_ for available options. e.g. Only access 3 floats if ImGuiColorEditFlags_NoAlpha flag is set.
 // With typical options: Left-click on color square to open color picker. Right-click to open option menu. CTRL-Click over input fields to edit them and TAB to go to next item.
@@ -4836,13 +4860,7 @@ bool ImGui::ColorEdit4(const char* label, float col[4], ImGuiColorEditFlags flag
     {
         // Hue is lost when converting from greyscale rgb (saturation=0). Restore it.
         ColorConvertRGBtoHSV(f[0], f[1], f[2], f[0], f[1], f[2]);
-        if (memcmp(g.ColorEditLastColor, col, sizeof(float) * 3) == 0)
+        ColorEditRestoreHS(col, &f[0], &f[1], &f[2]);
-        {
-            if (f[1] == 0)
-                f[0] = g.ColorEditLastHue;
-            if (f[2] == 0)
-                f[1] = g.ColorEditLastSat;
-        }
     }
     int i[4] = { IM_F32_TO_INT8_UNBOUND(f[0]), IM_F32_TO_INT8_UNBOUND(f[1]), IM_F32_TO_INT8_UNBOUND(f[2]), IM_F32_TO_INT8_UNBOUND(f[3]) };
 
@@ -4977,7 +4995,7 @@ bool ImGui::ColorEdit4(const char* label, float col[4], ImGuiColorEditFlags flag
             g.ColorEditLastHue = f[0];
             g.ColorEditLastSat = f[1];
             ColorConvertHSVtoRGB(f[0], f[1], f[2], f[0], f[1], f[2]);
-            memcpy(g.ColorEditLastColor, f, sizeof(float) * 3);
+            g.ColorEditLastColor = ColorConvertFloat4ToU32(ImVec4(f[0], f[1], f[2], 0));
         }
         if ((flags & ImGuiColorEditFlags_DisplayRGB) && (flags & ImGuiColorEditFlags_InputHSV))
             ColorConvertRGBtoHSV(f[0], f[1], f[2], f[0], f[1], f[2]);
@@ -5112,13 +5130,7 @@ bool ImGui::ColorPicker4(const char* label, float col[4], ImGuiColorEditFlags fl
     {
         // Hue is lost when converting from greyscale rgb (saturation=0). Restore it.
         ColorConvertRGBtoHSV(R, G, B, H, S, V);
-        if (memcmp(g.ColorEditLastColor, col, sizeof(float) * 3) == 0)
+        ColorEditRestoreHS(col, &H, &S, &V);
-        {
-            if (S == 0)
-                H = g.ColorEditLastHue;
-            if (V == 0)
-                S = g.ColorEditLastSat;
-        }
     }
     else if (flags & ImGuiColorEditFlags_InputHSV)
     {
@@ -5171,6 +5183,10 @@ bool ImGui::ColorPicker4(const char* label, float col[4], ImGuiColorEditFlags fl
         {
             S = ImSaturate((io.MousePos.x - picker_pos.x) / (sv_picker_size - 1));
             V = 1.0f - ImSaturate((io.MousePos.y - picker_pos.y) / (sv_picker_size - 1));
+
+            // Greatly reduces hue jitter and reset to 0 when hue == 255 and color is rapidly modified using SV square.
+            if (g.ColorEditLastColor == ColorConvertFloat4ToU32(ImVec4(col[0], col[1], col[2], 0)))
+                H = g.ColorEditLastHue;
             value_changed = value_changed_sv = true;
         }
         if (!(flags & ImGuiColorEditFlags_NoOptions))
@@ -5247,7 +5263,7 @@ bool ImGui::ColorPicker4(const char* label, float col[4], ImGuiColorEditFlags fl
             ColorConvertHSVtoRGB(H >= 1.0f ? H - 10 * 1e-6f : H, S > 0.0f ? S : 10 * 1e-6f, V > 0.0f ? V : 1e-6f, col[0], col[1], col[2]);
             g.ColorEditLastHue = H;
             g.ColorEditLastSat = S;
-            memcpy(g.ColorEditLastColor, col, sizeof(float) * 3);
+            g.ColorEditLastColor = ColorConvertFloat4ToU32(ImVec4(col[0], col[1], col[2], 0));
         }
         else if (flags & ImGuiColorEditFlags_InputHSV)
         {
@@ -5301,13 +5317,7 @@ bool ImGui::ColorPicker4(const char* label, float col[4], ImGuiColorEditFlags fl
             G = col[1];
             B = col[2];
             ColorConvertRGBtoHSV(R, G, B, H, S, V);
-            if (memcmp(g.ColorEditLastColor, col, sizeof(float) * 3) == 0) // Fix local Hue as display below will use it immediately.
+            ColorEditRestoreHS(col, &H, &S, &V);   // Fix local Hue as display below will use it immediately.
-            {
-                if (S == 0)
-                    H = g.ColorEditLastHue;
-                if (V == 0)
-                    S = g.ColorEditLastSat;
-            }
         }
         else if (flags & ImGuiColorEditFlags_InputHSV)
         {