Moderate spray can density based on time not CPU speed

Detail:
  The spray tool rate was ultimately determined by the number of wimp polls per second, which on a fast CPU can be 10,000's making the spray can more of a circle drawing tool.
  Use OS_ReadMonotonicTime to moderate the spray rate, so the speed of the CPU doesn't matter.
  Default density increased to 100 to achieve roughly the same density as a StrongARM Risc PC would previously.
Admin:
  Submission for the Paint bounty.

Version 2.21. Tagged as 'Paint-2_21'

VersionASM

@@ -11,13 +11,13 @@
                         GBLS    Module_HelpVersion
                         GBLS    Module_ComponentName
                         GBLS    Module_ComponentPath
-Module_MajorVersion     SETS    "2.20"
-Module_Version          SETA    220
+Module_MajorVersion     SETS    "2.21"
+Module_Version          SETA    221
 Module_MinorVersion     SETS    ""
-Module_Date             SETS    "14 Oct 2015"
-Module_ApplicationDate  SETS    "14-Oct-15"
+Module_Date             SETS    "20 May 2017"
+Module_ApplicationDate  SETS    "20-May-17"
 Module_ComponentName    SETS    "Paint"
 Module_ComponentPath    SETS    "castle/RiscOS/Sources/Apps/Paint"
-Module_FullVersion      SETS    "2.20"
-Module_HelpVersion      SETS    "2.20 (14 Oct 2015)"
+Module_FullVersion      SETS    "2.21"
+Module_HelpVersion      SETS    "2.21 (20 May 2017)"
                         END

VersionNum

-/* (2.20)
+/* (2.21)
  *
  * This file is automatically maintained by srccommit, do not edit manually.
  * Last processed by srccommit version: 1.1.
  *
  */
-#define Module_MajorVersion_CMHG        2.20
+#define Module_MajorVersion_CMHG        2.21
 #define Module_MinorVersion_CMHG        
-#define Module_Date_CMHG                14 Oct 2015
+#define Module_Date_CMHG                20 May 2017
 
-#define Module_MajorVersion             "2.20"
-#define Module_Version                  220
+#define Module_MajorVersion             "2.21"
+#define Module_Version                  221
 #define Module_MinorVersion             ""
-#define Module_Date                     "14 Oct 2015"
+#define Module_Date                     "20 May 2017"
 
-#define Module_ApplicationDate          "14-Oct-15"
+#define Module_ApplicationDate          "20-May-17"
 
 #define Module_ComponentName            "Paint"
 #define Module_ComponentPath            "castle/RiscOS/Sources/Apps/Paint"
 
-#define Module_FullVersion              "2.20"
-#define Module_HelpVersion              "2.20 (14 Oct 2015)"
-#define Module_LibraryVersionInfo       "2:20"
+#define Module_FullVersion              "2.21"
+#define Module_HelpVersion              "2.21 (20 May 2017)"
+#define Module_LibraryVersionInfo       "2:21"

c/Tools

@@ -68,10 +68,11 @@ static int  textxsize;
 static int  textysize;
 static int  textxspace;
 
-char        tools_spray_density [5] = "20";
+char        tools_spray_density [5] = "100";
 char        tools_spray_radius [5]  = "30";
 static int  spraydensity;
 static int  sprayradius;
+static int  spraytime = 0;
 
 /* SMC: The following are not sprite names. They are tokens which must be
  * used to look up the real sprite name in the Messages file.
@@ -2174,7 +2175,34 @@ static void spraycanpaint_splot (main_window *window, wimp_mousestr *mpos)
   /*Do nothing if radius == 0. J R C 5th Oct 1993*/
   if (sprayradius > 0)
   {
-    int pxs, pys;
+    int pxs, pys, elapsed, adjusted_density;
+    /*Adjust spray density according to CPU speed */
+    os_swix1r(OS_ReadMonotonicTime, 0, &elapsed);
+    if (spraytime > 0)
+    {
+      elapsed -= spraytime;
+      /*Divide this by a bigger constant to slow down the spray rate*/
+      adjusted_density = (spraydensity * elapsed) / 8;
+      if (adjusted_density > 0)
+      {
+        /*Reset the timer*/
+        spraytime += elapsed;
+        /*Sanity checks to stop unresponsiveness*/
+        if (adjusted_density > 999)
+          adjusted_density = 999;
+        if (adjusted_density > spraydensity * 2)
+          adjusted_density = spraydensity * 2;
+      }
+    }
+    else
+    {
+      /*Initial spray iteration*/
+      spraytime = elapsed;
+      adjusted_density = spraydensity / 10;
+    }
+
+    if (adjusted_density > 0)
+    {
       tools_mouse_to_pixel (window, mpos, &x, &y);
       pxs=tools_pixel_to_point_x(&window->data->sprite, 1);
       pys=tools_pixel_to_point_y(&window->data->sprite, 1);
@@ -2194,7 +2222,7 @@ static void spraycanpaint_splot (main_window *window, wimp_mousestr *mpos)
       domask = psprite_hasmask (sprite);
 
       visdelay_begin ();
-    for (i = 0; i < spraydensity; i++)
+      for (i = 0; i < adjusted_density; i++)
       { int r, nx, ny;
         double theta;
 
@@ -2232,6 +2260,7 @@ static void spraycanpaint_splot (main_window *window, wimp_mousestr *mpos)
 
       sprwindow_redisplay (sprite, &redraw_area);
     }
+  }
 }
 
 /***********************************************************
@@ -2273,7 +2302,11 @@ static void spraycanpaint_null (main_window *window, wimp_mousestr *mpos)
 
 { ftracef0 ("spraycanpaint_null\n");
   if (mpos->bbits == 0) /*if the mouse button is now up, stop tracking*/
+  {
     sprwindow_release_idle_events (window->data->sprite.sprite);
+    /*Reset spray timer*/
+    spraytime = 0;
+  }
   else
     spraycanpaint_splot (window, mpos);
 }