Clean up some arithmetic code in an example

The square root of a sum of squares is easier to read and should be
computed more accurately if done for us by hypot().  Variables set
only once should be set as an initializer and declared const, to make
clear this is what's happening.  Loop variables can be local to loops.
Adding a value to, or subtracting one from, a multiple of itself just
multiplies it be one plus (or minus) the multiplier; assigning the
result to the same variable is clearer as a *= (especially when the
factors are now overt numeric constants).  An array of 16k floats all
updated in locksteck to the same value can be replaced by a single
float that holds that value.  Simple things should not be needlessly
made more complicated - especially in example code, which should be
pedagogic.

Change-Id: Idab585cd7df1399c250d4b9f1396a085ae8f3864
Reviewed-by: hjk <hjk@qt.io>

1 files changed, 13 insertions, 17 deletions

diff --git a/examples/opengl/legacy/pbuffers2/glwidget.cpp b/examples/opengl/legacy/pbuffers2/glwidget.cpp
index 447461dbb3..c710d03cab 100644
--- a/examples/opengl/legacy/pbuffers2/glwidget.cpp
+++ b/examples/opengl/legacy/pbuffers2/glwidget.cpp
@@ -302,31 +302,27 @@ void GLWidget::timerEvent(QTimerEvent *)
     else if (!scale_in && scale < .5f)
         scale_in = true;
 
-    scale = scale_in ? scale + scale*0.01f : scale-scale*0.01f;
+    scale *= scale_in ? 1.01f : 0.99f;
     rot_z += 0.3f;
     rot_x += 0.1f;
 
-    int dx, dy; // disturbance point
-    float s, v, W;
-    int i, j;
-    static float wt[128][128];
+    static float wt = 0.0;
+    wt += 0.1f;
+
     const int width = logo.width();
+    const int dx = width >> 1, dy = dx; // disturbance point
+    const float v = -4; // wave speed
+    const float W = .3f;
     const int AMP = 5;
 
-    dx = dy = width >> 1;
-
-    W = .3f;
-    v = -4; // wave speed
-
-    for (i = 0; i < width; ++i) {
-        for ( j = 0; j < width; ++j) {
-            s = sqrt((double) ((j - dx) * (j - dx) + (i - dy) * (i - dy)));
-            wt[i][j] += 0.1f;
-            const double angle = 2 * M_PI * W * (wt[i][j] + s / v);
+    for (int i = 0; i < width; ++i) {
+        for (int j = 0; j < width; ++j) {
+            const float s = hypot(j - dx, i - dy);
+            const double raw = AMP * sin(2 * M_PI * W * (wt + s / v));
             if (s != 0)
-                wave[i * width + j] = AMP * sin(angle) / (0.2 * (s + 2));
+                wave[i * width + j] = raw / (0.2 * (s + 2));
             else
-                wave[i * width + j] = AMP * sin(angle);
+                wave[i * width + j] = raw;
         }
     }
 }