Android™ Application Development - Bahar Ali Khan

Chapter 11: Advanced Android Development
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while (rollDegree > 180 || rollDegree < -180)
{
if (rollDegree > 180) rollDegree = -180 + (rollDegree - 180);
if (rollDegree < -180) rollDegree = 180 - (rollDegree + 180);
}
6. Create paths that will fi ll each segment of the circle (ground and sky). The proportion of each
segment should be related to the clamped pitch.
Path skyPath = new Path();
skyPath.addArc(innerBoundingBox,
-tiltDegree,
(180 + (2 * tiltDegree)));
7. Spin the canvas around the center in the opposite direction to the current roll, and draw the sky
and ground paths using the Paints you created in Step 4.
canvas.rotate(-rollDegree, px, py);
canvas.drawOval(innerBoundingBox, groundPaint);
canvas.drawPath(skyPath, skyPaint);
canvas.drawPath(skyPath, markerPaint);
8. Next is the face marking. Start by calculating the start and end points for the horizontal horizon
markings.
int markWidth = radius / 3;
int startX = center.x - markWidth;
int endX = center.x + markWidth;
9. To make the horizon values easier to read, you should ensure that the pitch scale always starts
at the current value. The following code calculates the position of the interface between the
ground and sky on the horizon face:
double h = innerRadius*Math.cos(Math.toRadians(90-tiltDegree));
double justTiltY = center.y - h;
10. Find the number of pixels that represents each degree of tilt.
float pxPerDegree = (innerBoundingBox.height()/2)/45f;
11. Now iterate over 180 degrees, centered on the current tilt value, to give a sliding scale of possible
pitch.
for (int i = 90; i >= -90; i -= 10)
{
double ypos = justTiltY + i*pxPerDegree;
// Only display the scale within the inner face.
if ((ypos < (innerBoundingBox.top + textHeight)) ||
(ypos > innerBoundingBox.bottom - textHeight))
continue;
// Draw a line and the tilt angle for each scale increment.
canvas.drawLine(startX, (float)ypos, endX, (float)ypos, markerPaint);
int displayPos = (int)(tiltDegree - i);