Make slideshow objects' debugging semi-transparency and shift conditional

It was introduced in commit cfd7bf7f6e
(INTEGRATION: CWS presfixes12 (1.1.2); FILE ADDED, 2007-07-17); and
back then, it was guarded by VERBOSE define. The VERBOSE condition
was replaced by OSL_DEBUG_LEVEL >= 2 condition later in commit
912e36e911 (Remove VERBOSE part 3,
2012-04-10); and then, it was completely dropped in commit
e5ec630414 (stop inclduing
canvas/verbosetraces.hxx and canvas/debug.hxx, 2015-08-11).

But this code is definitely harmful by default, when an unaware
developer (like myself) tries to debug an animation problem, and
suddenly sees a very different problem in the debug build (the shift
and transparency of objects), which obviously is a new regression in
master, but it can't be bisected using bibisect repos, which makes
you to question your sanity, until you realize that it must be some
debug-only feature.

Thorsten wrote on IRC:
> the semi-transparency & shifting is needed for actually noticing
> what's behind (shapes get moved to sprites, then erased from the
> static canvas, then moved around)
> so I believe it's useful debugging tools, but of course should not
> randomly enable for normal dev builds

So use environment variable to control this behavior-changing code.

Change-Id: I493cdde26c95fdde4a5d542a0bdad8e329fdfda8
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/173965
Reviewed-by: Mike Kaganski <mike.kaganski@collabora.com>
Tested-by: Jenkins

slideshow/source/engine/slideview.cxx

@@ -23,6 +23,7 @@
 #include <eventqueue.hxx>
 #include <eventmultiplexer.hxx>
 #include <slideview.hxx>
+#include <tools.hxx>
 #include <delayevent.hxx>
 #include <unoview.hxx>
 
@@ -591,18 +592,17 @@ private:
                 mpSprite->setPriority(
                     maSpriteContainer.getLayerPriority().getMinimum() );
 
+                basegfx::B2DPoint pos(maLayerBoundsPixel.getMinimum());
+                double alpha = 1.0;
 #if defined(DBG_UTIL)
-                mpSprite->movePixel(
-                    basegfx::B2DPoint(maLayerBoundsPixel.getMinimum()) +
-                    basegfx::B2DPoint(10,10) );
-
-                mpSprite->setAlpha(0.5);
-#else
-                mpSprite->movePixel(
-                    basegfx::B2DPoint(maLayerBoundsPixel.getMinimum()) );
-
-                mpSprite->setAlpha(1.0);
+                if (isShowingMoreDebugInfo())
+                {
+                    pos += basegfx::B2DPoint(10, 10);
+                    alpha = 0.5;
+                }
 #endif
+                mpSprite->movePixel(pos);
+                mpSprite->setAlpha(alpha);
                 mpSprite->show();
             }
 

slideshow/source/engine/tools.cxx

@@ -776,6 +776,14 @@ namespace slideshow::internal
                 basegfx::fround( aTmpRect.getRange().getX() ) + 1,
                 basegfx::fround( aTmpRect.getRange().getY() ) + 1 );
         }
+
+#if defined(DBG_UTIL)
+bool isShowingMoreDebugInfo()
+{
+    static const bool bMoreInfo = getenv("SLIDESHOW_MORE_DEBUG_INFO") != nullptr;
+    return bMoreInfo;
+}
+#endif
 }
 
 /* vim:set shiftwidth=4 softtabstop=4 expandtab: */

slideshow/source/inc/tools.hxx

@@ -77,6 +77,10 @@ namespace slideshow
                 return hash_value(val);
             }
         };
+
+#if defined(DBG_UTIL)
+        bool isShowingMoreDebugInfo();
+#endif
     }
 }