limit core-plot min/max zoom - zooming

Question

I try to limit core-plot zoom between 2 value, more or less my code work, but sometime it don't work properly, this is the code:
- (void) handlePinchGesture:(UIPinchGestureRecognizer *)gestureRecognizer{
if (gestureRecognizer.state == UIGestureRecognizerStateBegan) {
scale = [gestureRecognizer scale];
}
else if (gestureRecognizer.state == UIGestureRecognizerStateChanged) {
CPTXYPlotSpace *plotSpace = (CPTXYPlotSpace *)self.graph.defaultPlotSpace;
lenghtX = [self getRoundedValue:max_X - min_X];
lenghtY = [self getRoundedValue:max_Y - min_Y];
if (lenghtX <= 100 && lenghtX >= 2) {
double stepScale = lenghtX / 10;
if ([gestureRecognizer scale] < scale) {
min_X = [self getRoundedValue:plotSpace.xRange.minLimitDouble - stepScale];
max_X = [self getRoundedValue:plotSpace.xRange.maxLimitDouble + stepScale];
min_Y = [self getRoundedValue:plotSpace.yRange.minLimitDouble - stepScale];
max_Y = [self getRoundedValue:plotSpace.yRange.maxLimitDouble + stepScale];
}
else {
min_X = [self getRoundedValue:plotSpace.xRange.minLimitDouble + stepScale];
max_X = [self getRoundedValue:plotSpace.xRange.maxLimitDouble - stepScale];
min_Y = [self getRoundedValue:plotSpace.yRange.minLimitDouble + stepScale];
max_Y = [self getRoundedValue:plotSpace.yRange.maxLimitDouble - stepScale];
}
}
else {
if (lenghtX > 100) {
double rest = [self getRoundedValue:(lenghtX - 100)/2];
min_X = [self getRoundedValue:min_X + rest];
max_X = [self getRoundedValue:max_X - rest];
min_Y = [self getRoundedValue:min_Y + rest];
max_Y = [self getRoundedValue:max_Y - rest];
NSLog(#"Lenght:%f Rest: %f",lenghtX,rest);
}
else if (lenghtX < 2) {
double rest = [self getRoundedValue:(2 - lenghtX)/2];
min_X = [self getRoundedValue:min_X - rest];
max_X = [self getRoundedValue:max_X + rest];
min_Y = [self getRoundedValue:min_Y - rest];
max_Y = [self getRoundedValue:max_Y + rest];
NSLog(#"Lenght:%f Rest: %f",lenghtX,rest);
}
}
lenghtX = [self getRoundedValue:max_X - min_X];
lenghtY = [self getRoundedValue:max_Y - min_Y];
NSLog(#"Lenght: %f",lenghtX);
plotSpace.xRange = [CPTPlotRange plotRangeWithLocation:CPTDecimalFromDouble(min_X) length:CPTDecimalFromFloat(lenghtX)];
plotSpace.yRange = [CPTPlotRange plotRangeWithLocation:CPTDecimalFromDouble(min_Y) length:CPTDecimalFromFloat(lenghtY)];
scale = [gestureRecognizer scale];
}
else if (gestureRecognizer.state == UIGestureRecognizerStateEnded) {
if (lenghtX <= 100 && lenghtX >= 2) {
CPTXYPlotSpace *plotSpace = (CPTXYPlotSpace *)self.graph.defaultPlotSpace;
min_X = [self getRoundedValue:plotSpace.xRange.minLimitDouble];
max_X = [self getRoundedValue:plotSpace.xRange.maxLimitDouble];
step_punto = (max_X-min_X)/numero_punti;
[self get_N_Value:numero_punti from:min_X toMax:max_X];
}
}
}
- (double) getRoundedValue:(double) value {
double roundedValue = round(value * 100.0) / 100.0;
return roundedValue;
}
In this code I check the length of visible x, if is >100 or <2 I set it 2 or 100, the problem is that not always the final value is inside this renege. The second problem is that when I zoom to the limit (for example when I zoom in) I want to block the zoom while now in the proximity of the limit there is a little zoom out and then a little zoom in (repeated).
How can I improve the code?

Answer 1

Remove the outer if-else statement that begins with if (lenghtX <= 100 && lenghtX >= 2). Always compute the scaled ranges and then check the length and adjust as necessary to bring it back in the 2-100 range.

Answer 2

You should check the accepted answer here:
Core Plot - set zoom level to show only part of graph
This is using global X and Y range setting. Which works perfectly for me.
There is also a mention in the comments for using the CPTPlotSpaceDelegate's method:
-(BOOL)plotSpace:(CPTPlotSpace *)space shouldScaleBy:(CGFloat)interactionScale aboutPoint:(CGPoint)interactionPoint;
Which would allow you to maintain a maximum zoom level. Note that minimum zoom level is actually handled by setting global X and Y ranges.