src/gui/node_editor.h: start implementing a node editor

src/gui/node_editor.h

@@ -0,0 +1,112 @@
+#pragma once
+
+#include <string>
+#include <vector>
+
+#define IMGUI_DEFINE_MATH_OPERATORS
+#include <imgui.h>
+#include <imgui_internal.h>
+
+#include "../geom.h"
+
+class GuiNode {
+public:
+    GuiNode(std::string name, Rect bbox)
+        : name(name), bbox(bbox)
+            {}
+
+protected:
+    friend class NodeEditor;
+
+    std::string name;
+
+    Rect bbox;
+};
+
+class NodeEditor {
+public:
+    NodeEditor() {
+        nodeList.emplace_back("hi", Rect(10, 10, 60, 60));
+        nodeList.emplace_back("hi2", Rect(10, 80, 60, 60));
+    }
+
+    void draw_window(const char *title, bool *opened) {
+        ImGui::SetNextWindowSize(ImVec2(700,600), ImGuiSetCond_FirstUseEver);
+        if (ImGui::Begin(title, opened)) {
+            // -- Create child canvas
+            ImGui::PushStyleVar(ImGuiStyleVar_FramePadding, ImVec2(1,1));
+            ImGui::PushStyleVar(ImGuiStyleVar_WindowPadding, ImVec2(0,0));
+            ImGui::PushStyleColor(ImGuiCol_ChildWindowBg, ImColor(60,60,70,200));
+            ImGui::BeginChild("nodes_region", ImVec2(0, 0), true, ImGuiWindowFlags_NoScrollbar|ImGuiWindowFlags_NoMove);
+
+            // -- Prepare to draw
+            // Get the draw list for this canvas
+            ImDrawList* draw_list = ImGui::GetWindowDrawList();
+            draw_list->ChannelsSplit(2);
+
+            // this gets the offset to the upper-right corner of the child canvas.
+            // Note: here, cursor means "draw cursor", not "mouse pointing cursor".
+            ImVec2 canvas_pos = ImGui::GetCursorScreenPos();
+            ImVec2 canvas_size = ImGui::GetWindowSize();
+
+            ImVec2 offset = canvas_pos - scrolling; // TODO: add scrolling
+
+            // -- Draw the grid
+            if (show_grid) {
+                ImVec2 local_offset = ImGui::GetCursorPos() - scrolling;
+
+                float spacing = 32.0f; ImU32 color = IM_COL32(200, 200, 200, 40);
+
+                for (float x = fmodf(local_offset.x, spacing); x < canvas_size.x; x += spacing)
+                    draw_list->AddLine(ImVec2(x, 0.0f)+canvas_pos,
+                                       ImVec2(x, canvas_size.y)+canvas_pos, color);
+                for (float y = fmodf(local_offset.y, spacing); y < canvas_size.y; y += spacing)
+                    draw_list->AddLine(ImVec2(0.0f, y)+canvas_pos,
+                                       ImVec2(canvas_size.x, y)+canvas_pos, color);
+            }
+
+            Rect viewportRect = Rect(scrolling, canvas_size);
+
+            for (const auto &node : nodeList) {
+                bool visible = viewportRect.intersects(node.bbox);
+                if (visible) {
+                    // -- Draw the node boxes
+                    draw_list->ChannelsSetCurrent(0); // Switch to the background layer
+
+                    ImVec2 upper_left = offset + node.bbox.pos;
+                    ImVec2 lower_right = upper_left + node.bbox.size;
+
+                    draw_list->AddRectFilled(upper_left, lower_right, ImColor(60, 60, 60), 4.0f);
+                    draw_list->AddRect(upper_left, lower_right, ImColor(100, 100, 100), 4.0f);
+
+                    // for (int i=0; i<N; i++) {
+                    //     auto position = node.bbox.pos;
+                    //     position.y += (i+1) * (node.bbox.size.y)/(N+1);
+
+                    //     draw_list->AddCircleFilled(offset + position, 4.0f, ImColor(150, 150, 150, 150));
+                    // }
+                }
+            }
+
+            // -- merge channels back together
+            draw_list->ChannelsMerge();
+
+            // -- scrolling!
+            //  [ pointer over neditor ]    [ not interacting ctrls ]    [    middle mouse dragging    ]
+            if (ImGui::IsWindowHovered() && !ImGui::IsAnyItemActive() && ImGui::IsMouseDragging(2, 0.0f))
+                scrolling = scrolling - ImGui::GetIO().MouseDelta;
+
+            // -- clean up
+            ImGui::EndChild();       // end :nodes_region
+            ImGui::PopStyleColor();  // pop ChildWindowBg
+            ImGui::PopStyleVar(2);   // pop FramePadding, WindowPadding
+        }
+        ImGui::End();
+    }
+
+private:
+    std::vector<GuiNode> nodeList;
+
+    ImVec2 scrolling = ImVec2(0.0f, 0.0f);
+    bool show_grid = true;
+};