draw guides for straightening

Program.cs

@@ -843,10 +843,10 @@ public class Game : GameWindow {
     // Load photos from a directory.
     // string[] files = Directory.GetFiles(@"c:\users\colin\desktop\photos-test\");
     // string[] files = Directory.GetFiles(@"c:\users\colin\pictures\photos\2023\07\14\");
-    // string[] files = Directory.GetFiles(@"c:\users\colin\pictures\photos\2023\09\06\jpg");
+    string[] files = Directory.GetFiles(@"c:\users\colin\pictures\photos\2023\09\06\jpg");
     // string[] files = Directory.GetFiles(@"G:\DCIM\100EOSR6\");
     // string[] files = Directory.GetFiles(@"c:\users\colin\desktop\totte-output\2023\08\03");
-    string[] files = Directory.GetFiles(@"c:\users\colin\desktop\export");
+    // string[] files = Directory.GetFiles(@"c:\users\colin\desktop\export");
     // string[] files = Directory.GetFiles(@"C:\Users\colin\Pictures\photos\2018\06\23");
     // string[] files = Directory.GetFiles(@"C:\Users\colin\Desktop\Germany all\104D7000");
     // string[] files = Directory.GetFiles(@"C:\Users\colin\Desktop\many-birds\");
@@ -1009,6 +1009,7 @@ public class Game : GameWindow {
     Photo activePhoto = photos[photoIndex];
     Texture active = activePhoto.Texture();
     bool cropActive = activeTool is CropTool;
+    bool straightenActive = activeTool is StraightenTool;
 
     // FIXME: make a function for scaling & centering one box on another.
     // FIXME: cropping is fucky because activeScale is using the texture size, not the photo size.
@@ -1036,7 +1037,11 @@ public class Game : GameWindow {
       Texture star = (activePhoto.Rating > i) ? STAR_FILLED : STAR_EMPTY;
       DrawTexture(star, geometry.StarBoxes[i].Min.X, geometry.StarBoxes[i].Min.Y);
     }
-    DrawCropRectangle(cropActive);
+    if (straightenActive) {
+      DrawStraightenGuides();
+    } else {
+      DrawCropRectangle(cropActive);
+    }
 
     // Draw thumbnail boxes.
     ribbonIndex = Math.Clamp(photoIndex - (geometry.ThumbnailBoxes.Count - 1) / 2,
@@ -1133,6 +1138,20 @@ public class Game : GameWindow {
     }
   }
 
+  void DrawStraightenGuides() {
+    Box2i box = geometry.PhotoBox;
+    int lineSpacing = 48;
+    Color4 color = new(1f, 1f, 1f, 0.5f);
+    for (int y = box.Min.Y + lineSpacing / 2; y < box.Max.Y; y += lineSpacing) {
+      DrawHorizontalLine(box.Min.X, y, box.Max.X, color);
+      // DrawHorizontalLine(box.Min.X, y + 1, box.Max.X, color);
+    }
+    for (int x = box.Min.X + lineSpacing / 2; x < box.Max.X; x += lineSpacing) {
+      DrawVerticalLine(x, box.Min.Y, box.Max.Y, color);
+      // DrawVerticalLine(x + 1, box.Min.Y, box.Max.Y, color);
+    }
+  }
+
   public void DrawTexture(Texture texture, int x, int y) {
     DrawTexture(texture, Util.MakeBox(x, y, texture.Size.X, texture.Size.Y));
   }