Fixed mouse wheel scroll issues, introduced a few weeks ago (#200)

imgui.cpp

@@ -547,6 +547,7 @@ static bool         CloseWindowButton(bool* p_opened = NULL);
 static void         FocusWindow(ImGuiWindow* window);
 static ImGuiWindow* FindHoveredWindow(ImVec2 pos, bool excluding_childs);
 static void         CloseInactivePopups();
+static void         SetWindowScrollY(ImGuiWindow* window, float scroll_y);
 
 // Helpers: String
 static int          ImStricmp(const char* str1, const char* str2);
@@ -2195,7 +2196,7 @@ void ImGui::NewFrame()
             if (!(window->Flags & ImGuiWindowFlags_NoScrollWithMouse))
             {
                 const int scroll_lines = (window->Flags & ImGuiWindowFlags_ComboBox) ? 3 : 5;
-                window->ScrollY -= g.IO.MouseWheel * window->CalcFontSize() * scroll_lines;
+                SetWindowScrollY(window, window->ScrollY - g.IO.MouseWheel * window->CalcFontSize() * scroll_lines);
             }
         }
     }
@@ -4028,6 +4029,7 @@ static void Scrollbar(ImGuiWindow* window)
         }
 
         // Apply scroll
+        // It is ok to modify ScrollY here because we are being called in Begin() after the calculation of SizeContents and before setting up our starting position
         const float scroll_y_norm = ImSaturate((clicked_y_norm - g.ScrollbarClickDeltaToGrabCenter - grab_h_norm*0.5f) / (1.0f - grab_h_norm));
         window->ScrollY = (float)(int)(0.5f + scroll_y_norm * (window->SizeContents.y - window->Size.y));
 
@@ -4374,6 +4376,13 @@ ImVec2 ImGui::GetWindowPos()
     return window->Pos;
 }
 
+static void SetWindowScrollY(ImGuiWindow* window, float new_scroll_y)
+{
+    window->DC.CursorMaxPos.y += window->ScrollY;
+    window->ScrollY = new_scroll_y;
+    window->DC.CursorMaxPos.y -= window->ScrollY;
+}
+
 static void SetWindowPos(ImGuiWindow* window, const ImVec2& pos, ImGuiSetCond cond)
 {
     // Test condition (NB: bit 0 is always true) and clear flags for next time
@@ -6933,8 +6942,8 @@ static bool InputTextEx(const char* label, char* buf, size_t buf_size, const ImV
         const bool is_ctrl_only = is_ctrl_down && !is_alt_down && !is_shift_down;
         if (IsKeyPressedMap(ImGuiKey_LeftArrow))                        { edit_state.OnKeyPressed(is_ctrl_down ? STB_TEXTEDIT_K_WORDLEFT | k_mask : STB_TEXTEDIT_K_LEFT | k_mask); }
         else if (IsKeyPressedMap(ImGuiKey_RightArrow))                  { edit_state.OnKeyPressed(is_ctrl_down ? STB_TEXTEDIT_K_WORDRIGHT | k_mask  : STB_TEXTEDIT_K_RIGHT | k_mask); }
-        else if (is_multiline && IsKeyPressedMap(ImGuiKey_UpArrow))     { if (is_ctrl_down) draw_window->ScrollY -= g.FontSize; else edit_state.OnKeyPressed(STB_TEXTEDIT_K_UP | k_mask); }
-        else if (is_multiline && IsKeyPressedMap(ImGuiKey_DownArrow))   { if (is_ctrl_down) draw_window->ScrollY += g.FontSize; else edit_state.OnKeyPressed(STB_TEXTEDIT_K_DOWN| k_mask); }
+        else if (is_multiline && IsKeyPressedMap(ImGuiKey_UpArrow))     { if (is_ctrl_down) SetWindowScrollY(draw_window, draw_window->ScrollY - g.FontSize); else edit_state.OnKeyPressed(STB_TEXTEDIT_K_UP | k_mask); }
+        else if (is_multiline && IsKeyPressedMap(ImGuiKey_DownArrow))   { if (is_ctrl_down) SetWindowScrollY(draw_window, draw_window->ScrollY + g.FontSize); else edit_state.OnKeyPressed(STB_TEXTEDIT_K_DOWN| k_mask); }
         else if (IsKeyPressedMap(ImGuiKey_Home))                        { edit_state.OnKeyPressed(is_ctrl_down ? STB_TEXTEDIT_K_TEXTSTART | k_mask : STB_TEXTEDIT_K_LINESTART | k_mask); }
         else if (IsKeyPressedMap(ImGuiKey_End))                         { edit_state.OnKeyPressed(is_ctrl_down ? STB_TEXTEDIT_K_TEXTEND | k_mask : STB_TEXTEDIT_K_LINEEND | k_mask); }
         else if (IsKeyPressedMap(ImGuiKey_Delete))                      { edit_state.OnKeyPressed(STB_TEXTEDIT_K_DELETE | k_mask); }