add curve demo pane

add a helper "HelpManipulateControlPoint" for control point manipulation

imgui_demo.cpp

@@ -187,6 +187,55 @@ static void HelpMarker(const char* desc)
     }
 }
 
+// Helper to interact with a control point
+// mouse left click/move for move the control point
+static ImVec2 HelpManipulateControlPoint(const int point_index, ImVec2& point_coords, const float point_radius, const ImVec4 canvas)
+{
+    static int selected_control_point = -1;
+
+    // current point control
+    ImVec2 point = ImVec2(canvas.x + point_coords.x * canvas.z, canvas.y + point_coords.y * canvas.w);
+
+    bool hovered = false;
+    if (ImGui::IsItemHovered())
+    {
+        if (ImGui::IsMouseHoveringRect(
+            ImVec2(point.x - point_radius * 0.5f, point.y - point_radius * 0.5f),
+            ImVec2(point.x + point_radius * 0.5f, point.y + point_radius * 0.5f)))
+        {
+            hovered = true;
+
+            // select if active and no point was selected before
+            // for have only one point movable at same time
+            if (selected_control_point < 0 && ImGui::IsItemActive())
+                selected_control_point = point_index;
+        }
+    }
+
+    ImDrawList* draw_list = ImGui::GetWindowDrawList();
+    // draw point background color
+    draw_list->AddCircleFilled(point, point_radius,
+        (selected_control_point == point_index) ? IM_COL32(0, 0, 255, 255) :
+        (hovered) ? IM_COL32(0, 127, 127, 255) : IM_COL32(255, 0, 0, 255));
+    // draw point edge
+    draw_list->AddCircle(point, point_radius, IM_COL32(255, 255, 255, 255), 0, 2.0f);
+
+    // unselect point
+    if (ImGui::IsMouseReleased(ImGuiMouseButton_Left))
+        selected_control_point = -1;
+
+    // move point, will be updated on next frame
+    if (selected_control_point == point_index &&
+        ImGui::IsMouseDragging(ImGuiMouseButton_Left, 0.0f))
+    {
+        ImGuiIO& io = ImGui::GetIO();
+        point_coords.x += io.MouseDelta.x / (canvas.z + 1e-5f);
+        point_coords.y += io.MouseDelta.y / (canvas.w + 1e-5f);
+    }
+
+    return point;
+}
+
 // Helper to display basic user controls.
 void ImGui::ShowUserGuide()
 {
@@ -7106,6 +7155,79 @@ static void ShowExampleAppCustomRendering(bool* p_open)
             ImGui::EndTabItem();
         }
 
+        if (ImGui::BeginTabItem("Curves"))
+        {
+            static ImVec2 bezier_control_points[4] = { ImVec2(0.12, 0.82), ImVec2(0.34, 0.21), ImVec2(0.90, 0.41), ImVec2(0.56, 0.82) }; // ratio of canvas size
+            static float control_point_radius = 10.0f;
+            static int curve_type = 0; // 0 quadratic, 1 cubic
+            static bool curve_segments_override = false;
+            static int curve_segments_override_v = 8;
+
+            ImGui::RadioButton("Quad Bezier", &curve_type, 0);
+            ImGui::SameLine(); HelpMarker("a Quad bezier have 3 control points;");
+            ImGui::SameLine(); ImGui::RadioButton("Cubic Bezier", &curve_type, 1);
+            ImGui::SameLine(); HelpMarker("a Cubic bezier have 4 control points;");
+            ImGui::Checkbox("##curvessegmentoverride", &curve_segments_override);
+            ImGui::SameLine(0.0f, ImGui::GetStyle().ItemInnerSpacing.x);
+            if (ImGui::SliderInt("Curves segments", &curve_segments_override_v, 3, 40))
+                curve_segments_override = true;
+
+            ImGui::Text("Mouse Left : move control points");
+
+            // canvas from last tab
+            // Using InvisibleButton() as a convenience 1) it will advance the layout cursor and 2) allows us to use IsItemHovered()/IsItemActive()
+            ImVec2 canvas_p0 = ImGui::GetCursorScreenPos();      // ImDrawList API uses screen coordinates!
+            ImVec2 canvas_sz = ImGui::GetContentRegionAvail();   // Resize canvas to what's available
+            if (canvas_sz.x < 50.0f) canvas_sz.x = 50.0f;
+            if (canvas_sz.y < 50.0f) canvas_sz.y = 50.0f;
+            ImVec2 canvas_p1 = ImVec2(canvas_p0.x + canvas_sz.x, canvas_p0.y + canvas_sz.y);
+
+            // Draw border and background color
+            ImGuiIO& io = ImGui::GetIO();
+            ImDrawList* draw_list = ImGui::GetWindowDrawList();
+            draw_list->AddRectFilled(canvas_p0, canvas_p1, IM_COL32(50, 50, 50, 255));
+            draw_list->AddRect(canvas_p0, canvas_p1, IM_COL32(255, 255, 255, 255));
+
+            // This will catch our interactions, only left button, no scrolling on this one
+            ImGui::InvisibleButton("canvas", canvas_sz, ImGuiButtonFlags_MouseButtonLeft);
+            ImVec4 canvas_rc = ImVec4(canvas_p0.x, canvas_p0.y, canvas_p1.x - canvas_p0.x, canvas_p1.y - canvas_p0.y);
+
+            draw_list->PushClipRect(canvas_p0, canvas_p1, true); // canvas clipping
+            {
+                draw_list->ChannelsSplit(2); // split channels
+
+                 // calc and render control point in top layer
+                draw_list->ChannelsSetCurrent(1);
+                ImVec2 cp[4]; // control point
+                for (int i = 0; i < 3 + curve_type; i++) // 3 when curve is quadratic, 4 when curve is cubic
+                {
+                    cp[i] = HelpManipulateControlPoint(i, bezier_control_points[i], control_point_radius, canvas_rc);
+                }
+
+                // render curve and edges in bottom layer
+                draw_list->ChannelsSetCurrent(0);
+                const ImU32 curve_color = IM_COL32(255, 255, 0, 255);
+                const int curve_segments = curve_segments_override ? curve_segments_override_v : 0;
+                if (curve_type) // bezier cubic
+                {
+                    draw_list->AddBezierCubic(cp[0], cp[1], cp[2], cp[3], curve_color, 2.0f, curve_segments); // curve
+                    draw_list->AddLine(cp[0], cp[1], IM_COL32(255, 255, 255, 255), 1.5f); // edge from control point 0 to 1
+                    draw_list->AddLine(cp[2], cp[3], IM_COL32(255, 255, 255, 255), 1.5f); // edge from control point 2 to 3
+                }
+                else // bezier quadratic
+                {
+                    draw_list->AddBezierQuadratic(cp[0], cp[1], cp[2], curve_color, 2.0f, curve_segments); // curve
+                    draw_list->AddLine(cp[0], cp[1], IM_COL32(255, 255, 255, 255), 1.5f); // edge from control point 0 to 1
+                    draw_list->AddLine(cp[1], cp[2], IM_COL32(255, 255, 255, 255), 1.5f); // edge from control point 2 to 3
+                }
+
+                draw_list->ChannelsMerge(); // merge channels
+            }
+            draw_list->PopClipRect();
+
+            ImGui::EndTabItem();
+        }
+
         ImGui::EndTabBar();
     }