From d15273051045da3c9d809979231832907a5cec7f Mon Sep 17 00:00:00 2001
From: AllyTally <alexiatilde@gmail.com>
Date: Thu, 9 Mar 2023 14:21:03 -0400
Subject: [PATCH] Add interpolation to tile tools

This uses DDA (https://w.wiki/6RSQ) to draw a line between the previous
frame's mouse position, and the current frame's mouse position. This
means that there will no longer be gaps in lines of tiles if you move
your mouse fast enough (which is actually rather slow, so it gets
annoying quickly).

The editor's timestep is no longer hardcoded to 24, as I assume that
was only done so there would be less gaps in lines of tiles drawn.
With interpolation, that is no longer an issue, so I've removed the
editor's special case for the timestep.
---
 desktop_version/src/Editor.cpp | 42 +++++++++++++++++++++++++++++-----
 desktop_version/src/Editor.h   |  1 +
 desktop_version/src/Game.cpp   |  2 --
 3 files changed, 37 insertions(+), 8 deletions(-)

diff --git a/desktop_version/src/Editor.cpp b/desktop_version/src/Editor.cpp
index 8e7c61b7..d66f2f81 100644
--- a/desktop_version/src/Editor.cpp
+++ b/desktop_version/src/Editor.cpp
@@ -81,6 +81,8 @@ void editorclass::reset(void)
     direct_mode_drawer = 0;
     entcol = 0;
 
+    old_tilex = 0;
+    old_tiley = 0;
     tilex = 0;
     tiley = 0;
     levx = 0;
@@ -1838,6 +1840,31 @@ int editorclass::get_entity_at(int xp, int yp)
     return -1;
 }
 
+static void set_tile_interpolated(const int x1, const int x2, const int y1, const int y2, const int tile)
+{
+    extern editorclass ed;
+
+    // draw a line between (x1, y1) and (x2, y2)
+
+    const int dx = x2 - x1;
+    const int dy = y2 - y1;
+
+    const int steps = SDL_max(abs(dx), abs(dy));
+
+    if (steps == 0)
+    {
+        ed.set_tile(x1, y1, tile);
+        return;
+    }
+
+    for (int i = 0; i <= steps; i++)
+    {
+        const int x = x1 + (dx * i) / steps;
+        const int y = y1 + (dy * i) / steps;
+
+        ed.set_tile(x, y, tile);
+    }
+}
 
 void editorclass::handle_tile_placement(const int tile)
 {
@@ -1848,7 +1875,7 @@ void editorclass::handle_tile_placement(const int tile)
         // Vertical line
         for (int i = 0; i < 30; i++)
         {
-            set_tile(tilex, i, tile);
+            set_tile_interpolated(old_tilex, tilex, i, i, tile);
         }
         return;
     }
@@ -1857,7 +1884,7 @@ void editorclass::handle_tile_placement(const int tile)
         // Horizontal line
         for (int i = 0; i < 40; i++)
         {
-            set_tile(i, tiley, tile);
+            set_tile_interpolated(i, i, old_tiley, tiley, tile);
         }
         return;
     }
@@ -1879,7 +1906,7 @@ void editorclass::handle_tile_placement(const int tile)
     }
     else
     {
-        set_tile(tilex, tiley, tile);
+        set_tile_interpolated(old_tilex, tilex, old_tiley, tiley, tile);
         return;
     }
 
@@ -1887,7 +1914,7 @@ void editorclass::handle_tile_placement(const int tile)
     {
         for (int j = -range; j <= range; j++)
         {
-            set_tile(tilex + i, tiley + j, tile);
+            set_tile_interpolated(old_tilex + i, tilex + i, old_tiley + j, tiley + j, tile);
         }
     }
 }
@@ -1901,7 +1928,7 @@ void editorclass::tool_remove()
         handle_tile_placement(0);
         break;
     case EditorTool_SPIKES:
-        set_tile(tilex, tiley, 0);
+        set_tile_interpolated(old_tilex, tilex, old_tiley, tiley, 0);
         break;
     default:
         break;
@@ -2015,7 +2042,7 @@ void editorclass::tool_place()
         break;
     }
     case EditorTool_SPIKES:
-        set_tile(tilex, tiley, 8);
+        set_tile_interpolated(old_tilex, tilex, old_tiley, tiley, 8);
         break;
     case EditorTool_TRINKETS:
         if (cl.numtrinkets() < 100)
@@ -2624,6 +2651,9 @@ void editorinput(void)
         return;
     }
 
+    ed.old_tilex = ed.tilex;
+    ed.old_tiley = ed.tiley;
+
     ed.tilex = (key.mx - (key.mx % 8)) / 8;
     ed.tiley = (key.my - (key.my % 8)) / 8;
 
diff --git a/desktop_version/src/Editor.h b/desktop_version/src/Editor.h
index 9322aad4..913cde20 100644
--- a/desktop_version/src/Editor.h
+++ b/desktop_version/src/Editor.h
@@ -195,6 +195,7 @@ public:
     std::string filename;
     std::string loaded_filepath;
 
+    int old_tilex, old_tiley;
     int tilex, tiley;
     int keydelay, lclickdelay;
     bool savekey, loadkey;
diff --git a/desktop_version/src/Game.cpp b/desktop_version/src/Game.cpp
index e668b051..b8876a88 100644
--- a/desktop_version/src/Game.cpp
+++ b/desktop_version/src/Game.cpp
@@ -7365,8 +7365,6 @@ int Game::get_timestep(void)
 {
     switch (gamestate)
     {
-    case EDITORMODE:
-        return 24;
     case GAMEMODE:
         return get_framerate(slowdown);
     default: