From 6a5cad3dbc10e2cafd95269402a92fda34d01385 Mon Sep 17 00:00:00 2001
From: Even Rouault <even.rouault@spatialys.com>
Date: Thu, 12 Oct 2017 14:39:28 +0200
Subject: [PATCH] msLayerIsVisible(): speed it up by doing layer vs map scale
 comparisons before extent comparison

---
 mapdraw.c | 31 ++++++++++++++++++-------------
 1 file changed, 18 insertions(+), 13 deletions(-)

diff --git a/mapdraw.c b/mapdraw.c
index 01848199ea..41ac8903dd 100644
--- a/mapdraw.c
+++ b/mapdraw.c
@@ -594,17 +594,8 @@ int msLayerIsVisible(mapObj *map, layerObj *layer)
   if(layer->type == MS_LAYER_QUERY || layer->type == MS_LAYER_TILEINDEX) return(MS_FALSE);
   if((layer->status != MS_ON) && (layer->status != MS_DEFAULT)) return(MS_FALSE);
 
-  /* Only return MS_FALSE if it is definitely false. Sometimes it will return MS_UNKNOWN, which we
-  ** consider true, for this use case (it might be visible, try and draw it, see what happens). */
-  if ( msExtentsOverlap(map, layer) == MS_FALSE ) {
-    if( layer->debug >= MS_DEBUGLEVEL_V ) {
-      msDebug("msLayerIsVisible(): Skipping layer (%s) because LAYER.EXTENT does not intersect MAP.EXTENT\n", layer->name);
-    }
-    return(MS_FALSE);
-  }
-
-  if(msEvalContext(map, layer, layer->requires) == MS_FALSE) return(MS_FALSE);
-
+  /* Do comparisons of layer scale vs map scale now, since msExtentsOverlap() */
+  /* can be slow */
   if(map->scaledenom > 0) {
 
     /* layer scale boundaries should be checked first */
@@ -614,13 +605,27 @@ int msLayerIsVisible(mapObj *map, layerObj *layer)
       }
       return(MS_FALSE);
     }
-    if((layer->minscaledenom > 0) && (map->scaledenom <= layer->minscaledenom)) {
+    if(/*(layer->minscaledenom > 0) &&*/ (map->scaledenom <= layer->minscaledenom)) {
       if( layer->debug >= MS_DEBUGLEVEL_V ) {
         msDebug("msLayerIsVisible(): Skipping layer (%s) because LAYER.MINSCALE is too large for this MAP scale\n", layer->name);
       }
       return(MS_FALSE);
     }
-  
+  }
+
+  /* Only return MS_FALSE if it is definitely false. Sometimes it will return MS_UNKNOWN, which we
+  ** consider true, for this use case (it might be visible, try and draw it, see what happens). */
+  if ( msExtentsOverlap(map, layer) == MS_FALSE ) {
+    if( layer->debug >= MS_DEBUGLEVEL_V ) {
+      msDebug("msLayerIsVisible(): Skipping layer (%s) because LAYER.EXTENT does not intersect MAP.EXTENT\n", layer->name);
+    }
+    return(MS_FALSE);
+  }
+
+  if(msEvalContext(map, layer, layer->requires) == MS_FALSE) return(MS_FALSE);
+
+  if(map->scaledenom > 0) {
+
     /* now check class scale boundaries (all layers *must* pass these tests) */
     if(layer->numclasses > 0) {
       for(i=0; i<layer->numclasses; i++) {