1 files changed, 104 insertions, 19 deletions

diff --git a/src/ui.cpp b/src/ui.cpp
index 8e4e275..f870a24 100644
--- a/src/ui.cpp
+++ b/src/ui.cpp
@@ -5,17 +5,11 @@
 #include <imgui.h>
 #include <memory>
 
-static void AddSand(Sandbox& sb) {
-    for (int y = 80; y <= 90; ++y) {
-        for (int x = 10; x <= 13; ++x) {
-            sb.set_sand(x, y, Tile{ .so = Tile::SAND });
-        }
-    }
-}
-
+// NOTE: also exists in imgui_internal.h
+// intentionally name it the same (including the fields), so if somebody else comes along and includes imgui_internal.h, they get a compile error and they can remove this
 struct ImRect {
-    ImVec2 top_left;
-    ImVec2 bottom_right;
+    ImVec2 Min;
+    ImVec2 Max;
 };
 
 /// Helpers for displaying and coordinate space tracking of the sandbox image display.
@@ -25,6 +19,8 @@ struct SandboxDisplay {
     int sandbox_height = 100;
 
     ImVec2 size_screenspace;
+
+    /* AVAILABLE AFTER CALLING show_image() */
     ImVec2 origin;
 
     SandboxDisplay(float tile_size, const Sandbox& sb)
@@ -45,15 +41,62 @@ struct SandboxDisplay {
         };
     }
 
+    // `pos` is +X right, +Y down from top left of the window's content region
+    Pt tr_screen2sandbox(ImVec2 pos) const {
+        // +X right, +Y up from `origin`
+        ImVec2 translated(pos.x - origin.x, origin.y - pos.y);
+        return Pt(translated.x / tile_size, translated.y / tile_size);
+    }
+
+    bool is_out_of_bounds(Pt pt) const {
+        return pt.x < 0 || pt.x >= sandbox_width || pt.y < 0 || pt.y >= sandbox_height;
+    }
+
     void show_image(ImTextureID texid) {
         auto img_topleft = ImGui::GetCursorScreenPos();
-        ImGui::Image(texid, size_screenspace, ImVec2(0, 1), ImVec2(1, 0));
+        ImGui::InvisibleButton("sandbox", size_screenspace);
+        const auto rect_min = ImGui::GetItemRectMin();
+        const auto rect_max = ImGui::GetItemRectMax();
+        ImGui::GetWindowDrawList()->AddImage(texid, rect_min, rect_max, ImVec2(0, 1), ImVec2(1, 0));
+
         // bottom-left corner of the sandbox, in screen space
-        origin = img_topleft;
+        origin = rect_min;
         origin.y += size_screenspace.y;
     }
 };
 
+typedef int BrushType;
+enum BrushType_ {
+    BrushType_Box,
+    BrushType_Circle,
+};
+
+static void paint_sand(Sandbox& sb, const Tile& palette, Pt pt, BrushType type, int size) {
+    switch (type) {
+    case BrushType_Box: {
+        // size: side length
+        int y0 = pt.y - size / 2;
+        int x0 = pt.x - size / 2;
+        for (int y = y0; y < y0 + size; ++y) {
+            for (int x = x0; x < x0 + size; ++x) {
+                sb.set_sand(x, y, palette);
+            }
+        }
+    } break;
+
+    case BrushType_Circle: {
+        // size: radius
+        // TODO
+    } break;
+
+    default: {
+        ImGui::PushStyleColor(ImGuiCol_Text, IM_COL32(255, 0, 0, 255));
+        ImGui::Text("invalid brush type %d", type);
+        ImGui::PopStyleVar();
+    } break;
+    }
+}
+
 void ShowEverything() {
     ImGui::Begin("Options");
 
@@ -92,22 +135,27 @@ void ShowEverything() {
     ImGui::Checkbox("Run", &running);
     static bool show_dirty_rect = true;
     ImGui::Checkbox("Show dirty rects", &show_dirty_rect);
+    static bool hide_mouse = true;
+    ImGui::Checkbox("Hide mouse", &hide_mouse);
 
     ImGui::Text("ncycle = %d", sandbox->ncycle);
     ImGui::SameLine();
     bool step = ImGui::Button("Step");
 
-    if (step || running) {
-        sandbox->simulate_step();
-    }
+    static Tile palette{ .so = Tile::SAND };
+    static int brush_size = 1;
+    static BrushType brush_type = BrushType_Box;
 
-    if (ImGui::Button("Add sand")) {
-        AddSand(*sandbox);
-    }
+    ImGui::SliderInt("Brush radius", &brush_size, 1, 20);
+    ImGui::Combo("Brush type",
+        &brush_type,
+        "Box\0"
+        "Circle");
 
     ImGui::End();
 
     ImGui::Begin("Sandbox");
+
     // Update texture to the current state of the the sandbox.
     // Do this every frame, because it's easier than trying to track when did the sandbox change, which may be caused by:
     // - Initialization
@@ -118,11 +166,48 @@ void ShowEverything() {
     SandboxDisplay dis(tile_size, *sandbox);
     dis.show_image(gl.as_imgui());
 
+    auto dl = ImGui::GetWindowDrawList();
+
     if (show_dirty_rect) {
-        auto dl = ImGui::GetWindowDrawList();
         auto [top_left, bottom_right] = dis.tr_sandbox2screen(sandbox->dirty_writeto);
         dl->AddRect(top_left, bottom_right, IM_COL32(255, 0, 0, 255));
     }
+
+    // Unfortunate technical limitation: update HAS to come after render
+    // We don't get the screen pos of the ImGui::Image after having called it
+
+    if (step || running) {
+        sandbox->simulate_step();
+    }
+
+    // HERE BE DRAGON: poor man's inner function
+    do {
+        // This checks for popup windows, drag&drop state, overlapping widgets, etc.
+        // So it's necessary even if tr_screen2sandbox() can already detect if the mouse is out of bounds
+        if (!ImGui::IsItemHovered())
+            break;
+
+        if (hide_mouse) {
+            ImGui::SetMouseCursor(ImGuiMouseCursor_None);
+        }
+
+        auto mouse_pt = dis.tr_screen2sandbox(ImGui::GetMousePos());
+        // This does trigger, if mouse is at very top of the image
+        // There must be some discrepency between the math above, and ImGui's hover rect calculation. I'm not sure what's happening.
+        if (dis.is_out_of_bounds(mouse_pt))
+            break;
+
+        // Show the tile under mouse
+        auto [top_left, bottom_right] = dis.tr_sandbox2screen(Rect(mouse_pt, mouse_pt));
+        dl->AddRect(top_left, bottom_right, IM_COL32_BLACK);
+
+        if (ImGui::IsItemActive()) {
+            paint_sand(*sandbox, palette, mouse_pt, brush_type, brush_size);
+        }
+
+        break;
+    } while (false);
+
     ImGui::End();
 
     ImGui::ShowDemoWindow();