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Clean up some arithmetic code in an example

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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>
This commit is contained in:
Edward Welbourne 2017-03-22 15:25:32 +01:00
parent fdfa3b1141
commit 29af390e3f
1 changed files with 13 additions and 17 deletions
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30
examples/opengl/legacy/pbuffers2/glwidget.cpp
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@ -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;
}
}
}