ColorPicker: added option to fix Saturation/Value triangle in wheel picker. (#9337)

imgui.h

diff --git a/imgui.h b/imgui.h
index caae045..c1a74f5 100644
--- a/imgui.h
+++ b/imgui.h
@@ -1914,8 +1914,9 @@
     ImGuiColorEditFlags_Float           = 1 << 24,  // [DataType]   // ColorEdit, ColorPicker, ColorButton: _display_ values formatted as 0.0f..1.0f floats instead of 0..255 integers. No round-trip of value via integers.
     ImGuiColorEditFlags_PickerHueBar    = 1 << 25,  // [Picker]     // ColorPicker: bar for Hue, rectangle for Sat/Value.
     ImGuiColorEditFlags_PickerHueWheel  = 1 << 26,  // [Picker]     // ColorPicker: wheel for Hue, triangle for Sat/Value.
-    ImGuiColorEditFlags_InputRGB        = 1 << 27,  // [Input]      // ColorEdit, ColorPicker: input and output data in RGB format.
-    ImGuiColorEditFlags_InputHSV        = 1 << 28,  // [Input]      // ColorEdit, ColorPicker: input and output data in HSV format.
+    ImGuiColorEditFlags_FixedTriangle   = 1 << 27,  // [Picker]     // ColorPicker: fix triangle position for PickerHueWheel.
+    ImGuiColorEditFlags_InputRGB        = 1 << 28,  // [Input]      // ColorEdit, ColorPicker: input and output data in RGB format.
+    ImGuiColorEditFlags_InputHSV        = 1 << 29,  // [Input]      // ColorEdit, ColorPicker: input and output data in HSV format.
 
     // Defaults Options copied to io.ConfigColorEditFlags during initialization.
     // The intent is that you probably don't want to override them in most of your calls.

imgui_widgets.cpp

diff --git a/imgui_widgets.cpp b/imgui_widgets.cpp
index 6276f7d..d4e3926 100644
--- a/imgui_widgets.cpp
+++ b/imgui_widgets.cpp
@@ -6130,6 +6130,12 @@
     ImVec2 triangle_pa = ImVec2(triangle_r, 0.0f); // Hue point.
     ImVec2 triangle_pb = ImVec2(triangle_r * -0.5f, triangle_r * -0.866025f); // Black point.
     ImVec2 triangle_pc = ImVec2(triangle_r * -0.5f, triangle_r * +0.866025f); // White point.
+    if (flags & ImGuiColorEditFlags_FixedTriangle)
+    {
+        triangle_pa = ImVec2(triangle_r * +0.866025f, triangle_r * +0.5f); // Hue point.
+        triangle_pb = ImVec2(0.0f, -triangle_r); // Black point.
+        triangle_pc = ImVec2(triangle_r * -0.866025f, triangle_r * +0.5f); // White point.
+    }
 
     float H = col[0], S = col[1], V = col[2];
     float R = col[0], G = col[1], B = col[2];
@@ -6166,6 +6172,11 @@
             }
             float cos_hue_angle = ImCos(-H * 2.0f * IM_PI);
             float sin_hue_angle = ImSin(-H * 2.0f * IM_PI);
+            if (flags & ImGuiColorEditFlags_FixedTriangle)
+            {
+                cos_hue_angle = ImCos(-0.0 * 2.0f * IM_PI);
+                sin_hue_angle = ImSin(-0.0 * 2.0f * IM_PI);
+            }
             if (ImTriangleContainsPoint(triangle_pa, triangle_pb, triangle_pc, ImRotate(initial_off, cos_hue_angle, sin_hue_angle)))
             {
                 // Interacting with SV triangle
@@ -6374,6 +6385,11 @@
         draw_list->AddCircleFilled(hue_cursor_pos, hue_cursor_rad, hue_color32, hue_cursor_segments);
         draw_list->AddCircle(hue_cursor_pos, hue_cursor_rad + 1, col_midgrey, hue_cursor_segments);
         draw_list->AddCircle(hue_cursor_pos, hue_cursor_rad, col_white, hue_cursor_segments);
+        if (flags & ImGuiColorEditFlags_FixedTriangle)
+        {
+            cos_hue_angle = ImCos(-0.0 * 2.0f * IM_PI);
+            sin_hue_angle = ImSin(-0.0 * 2.0f * IM_PI);
+        }
 
         // Render SV triangle (rotated according to hue)
         ImVec2 tra = wheel_center + ImRotate(triangle_pa, cos_hue_angle, sin_hue_angle);