How do I manage the drawing of custom data (not photos) in an NSView that has an area dynamically larger than what is viewable? - objective-c

Question

UPDATE: Relative to the questions and answers below, it seems I have a misunderstanding of the NSView class in relation to the custom classes I'm trying to draw and the wrapping NSScrollView. In the end, what I'm trying to figure out is how do I manage the dynamic drawing of custom data (not photos) in an NSView that has an area larger than what is viewable?
I am not looking for a handout, but I am a novice to Cocoa and I thought I was doing best-practice based on Apple's docs, but it seems I've gotten the fundamentals wrong. Apple's documentation is incredibly detailed, technical, centered entirely around working with photos, and thus useless to me. The related code examples provided by Apple (e.g. Sketch) get the document size from the printer paper sizes in their typically oblique fashion, and that's not what I need. I've scoured the web for tutorials, examples and the like, but I'm not finding much of anything (and I promise to write one when I get this sorted out).
I'm porting this code from REALbasic where I have this completely working, even with Undo commands, but the paradigms to do so are entirely different. This just isn't "clicking" for me. I appreciate the help given, I'm still missing something here, anything else folks have to offer is appreciated.
Thanks
I have a subclassed NSView where I'm creating a piano-roll MIDI interface. I am trying to resolve a few problems:
Drawing artifacts during and after scrolling
Lines not spanning across the visible area during and after scrolling
While scrolling and sometimes on mouseDown, the horizontal scroller jumps to the right 1 (one) pixel, but I don't have scrollToPoint implemented anywhere yet.
Symptoms that relate to the above:
Implementing adjustScroll makes everything worse.
mouseDown corrects all of the problems except sometimes the 1-pixel jump to the right.
If I uncomment the NSLog command the beginning of drawRect nothing draws.
Apple's documentation mentions pixel-accurate drawing, but (of course) offers up no examples on how this can be achieved. I've been using the floor() function to try to get consistent values, but once I start tacking on scrollToPoint or any other complexity, things go haywire.
Please see the linked image as an example. The screenshot, if you can believe it, actually cleans up what I see on screen. There are double lines almost everywhere at half opacity as well. The same is applied to any objects I draw as well.
Graphics Artifacts and inconsistencies in a subclassed NSView generated after scrolling http://www.oatmealandcoffee.com/external/NSViewArtifacts.png
Here is the code. I hate giving up so much publicly, but I've searched everywhere for clues, and if the Internet is any indication I'm the only person with this problem, and I really just want to get this sorted out and move forward. There is a lot, and there is more to come, but these is the core stuff I really need to get right, and, frankly, I am at a loss on how to correct it.
- (void)drawRect:(NSRect)rect {
//NSLog(#"OCEditorView:drawRect: START");
[self setFrame:[[self EditorDocument] DocumentRect]];
[[NSGraphicsContext currentContext] setShouldAntialias:NO];
// CLEAR BACKGROUND
[[[self EditorDocument] ColorWhiteKey] set];
NSRectFill(rect);
// BACKGROUND KEYS
int firstRowLine = 0; //NSMinY(rect); //<- adding the function results in bad spacing on scrolling
int currentRowLine = 0;
int lastRowLine = NSMaxY(rect);
//NSLog(#"lastRowLine:%d", lastRowLine);
float currentZoomY = [self ZoomY];
for (currentRowLine = firstRowLine; currentRowLine <= lastRowLine; currentRowLine += currentZoomY) {
int currentTone = floor(currentRowLine / [self ZoomY]);
BOOL isBlackKey = [[self MusicLib] IsBlackKey:currentTone];
//NSLog(#"%d, tone:%d, black:%d", [self MusicLib], currentTone, isBlackKey);
if (isBlackKey) {
[[[self EditorDocument] ColorBlackKey] set];
} else {
[[NSColor whiteColor] set];
}
NSBezierPath *rowLine = [NSBezierPath bezierPath];
NSPoint bottomLeftPoint = NSMakePoint(NSMinX(rect), currentRowLine);
NSPoint bottomRightPoint = NSMakePoint(NSMaxX(rect), currentRowLine);
NSPoint topRightPoint = NSMakePoint(NSMaxX(rect), currentRowLine + [self ZoomY]);
NSPoint topLeftPoint = NSMakePoint(NSMinX(rect), currentRowLine + [self ZoomY]);
[rowLine moveToPoint:bottomLeftPoint];
[rowLine lineToPoint:bottomRightPoint];
[rowLine lineToPoint:topRightPoint];
[rowLine lineToPoint:topLeftPoint];
[rowLine closePath];
[rowLine fill];
BOOL isOctave = [[self MusicLib] IsOctave:currentTone];
if (isOctave) {
[[[self EditorDocument] ColorXGrid] set];
NSBezierPath *octaveLine = [NSBezierPath bezierPath];
NSPoint leftPoint = NSMakePoint(NSMinX(rect), currentRowLine);
NSPoint rightPoint = NSMakePoint(NSMaxX(rect), currentRowLine);
[octaveLine moveToPoint:leftPoint];
[octaveLine lineToPoint:rightPoint];
[octaveLine stroke];
}
}
// BACKGROUND MEASURES
//[[self EditorDocument].ColorYGrid setStroke];
int firstColumnLine = 0;
int currentColumnLine = 0;
int lastColumnLine = NSMaxX(rect);
int snapToValueInBeats = [[self EditorDocument] SnapToValue];
int snapToValueInPixels = floor(snapToValueInBeats * [self ZoomX]);
int measureUnitInBeats = floor([[self EditorDocument] TimeSignatureBeatsPerMeasure] * [[self EditorDocument] TimeSignatureBasicBeat]);
int measureUnitInPixels = floor(measureUnitInBeats * [self ZoomX]);
for (currentColumnLine = firstColumnLine; currentColumnLine <= lastColumnLine; currentColumnLine += snapToValueInPixels) {
//int currentBeat = floor(currentColumnLine / [self ZoomX]);
int isAMeasure = currentColumnLine % measureUnitInPixels;
int isAtSnap = currentColumnLine % snapToValueInPixels;
if ((isAMeasure == 0) || (isAtSnap == 0)) {
if (isAtSnap == 0) {
[[NSColor whiteColor] set];
}
if (isAMeasure == 0) {
[[[self EditorDocument] ColorXGrid] set];
}
NSBezierPath *columnLine = [NSBezierPath bezierPath];
NSPoint startPoint = NSMakePoint(currentColumnLine, NSMinY(rect));
NSPoint endPoint = NSMakePoint(currentColumnLine, NSMaxY(rect));
[columnLine moveToPoint:startPoint];
[columnLine lineToPoint:endPoint];
[columnLine setLineWidth:1.0];
[columnLine stroke];
} // isAMeasure or isAtSnap
} // currentColumnLine
// NOTES
for (OCNoteObject *note in [[self EditorDocument] Notes]) {
OCNoteObject *currentNote = note;
NSRect noteBounds = [self GetRectFromNote:currentNote];
//NSLog(#"noteBounds:%d", noteBounds);
// set the color for the note fill
// this will have to come from the parent Track
NSMutableArray *trackColors = [self EditorDocument].TrackColors;
if (note.Selected) {
[[trackColors objectAtIndex:0] set];
} else {
[[trackColors objectAtIndex:1] set];
}
[NSBezierPath fillRect:noteBounds];
// outline
[[NSColor blackColor] set];
[NSBezierPath strokeRect:noteBounds];
} // for each note
/*
if (EditorController.startingUpApplication == YES) {
[self setDefaultSettingForApplicationStartUp];
}
*/
//NSLog(#"OCEditorView:drawRect: END");
}
- (void)mouseDown:(NSEvent *)theEvent {
//NSLog(#"OCEditorObject:mouseDown: START");
// This converts the click into coordinates
MouseDownPoint = [self convertPoint:[theEvent locationInWindow] fromView:nil];
// Calculate the beat and pitch clicked into...
float startBeat = floor(MouseDownPoint.x / [self ZoomX]);
float pitch = floor(MouseDownPoint.y / [self ZoomY]);
float length = [[self EditorDocument] NewNoteLength];
//NSLog(#"X:%f, Y:%f", MouseDownPoint.x, MouseDownPoint.y);
//NSLog(#"beat:%f, pitch:%f", startBeat, pitch);
LastDragPoint = MouseDownPoint; // save the point just in case.
OCNoteObject *note = [self GetClickedNoteFromPoint:MouseDownPoint];
if ([EditorController EditorMode] == AddObjectMode) {
//NSLog(#"AddObjectMode)");
float snapToX = [[self EditorDocument] SnapToValue];
float snappedStartBeat = floor(startBeat / snapToX) * snapToX;
//NSLog(#"%f = %f / %f * %f", snappedStartBeat, startBeat, snapToX, snapToX);
OCNoteObject *newNote = [[self EditorDocument] CreateNote:snappedStartBeat Pitch:pitch Length:length];
//NSLog(#"newNote:%d", newNote);
[newNote Deselect];
} else if ([EditorController EditorMode] == EditObjectMode) {
//NSLog(#"EditObjectMode");
// if nothing was clicked, then clear the selections
// else if the shift key was pressed, add to the selection
if (note == nil) {
[self SelectNone];
} else {
//NSLog(#"mouseDown note.pitch:%f, oldPitch:%f", note.Pitch, note.OldPitch);
BOOL editingSelection = (([theEvent modifierFlags] & NSShiftKeyMask) ? YES : NO);
if (editingSelection) {
if (note.Selected) {
[self RemoveFromSelection:note];
} else {
[self AddToSelection:note];
}
} else {
if (note.Selected) {
// do nothing
} else {
[self SelectNone];
[self AddToSelection:note];
}
}
[self SetOldData];
} // (note == nil)
} else if ([EditorController EditorMode] == DeleteObjectMode) {
if (note != nil) {
[self RemoveFromSelection:note];
[[self EditorDocument] DestroyNote:note];
} // (note != nil)
} // EditorMode
[self setFrame:[[self EditorDocument] DocumentRect]];
[self setNeedsDisplay:YES];
}
- (void)mouseDragged:(NSEvent *)theEvent {
//NSLog(#"mouseDragged");
NSPoint currentDragPoint = [self convertPoint:[theEvent locationInWindow] fromView:nil];
// NSLog(#"currentDragPoint: %d", currentDragPoint)
float snapToValueInBeats = [[self EditorDocument] SnapToValue];
int deltaXinPixels = floor(currentDragPoint.x - MouseDownPoint.x);
int deltaYinPixels = floor(currentDragPoint.y - MouseDownPoint.y);
int deltaXinBeats = floor(deltaXinPixels / [self ZoomX]);
int deltaY = floor(deltaYinPixels / [self ZoomY]);
int deltaX = floor(deltaXinBeats / snapToValueInBeats) * snapToValueInBeats;
for (OCNoteObject *note in [self Selection]) {
[self MoveNote:note DeltaX:deltaX DeltaY:deltaY];
}
LastDragPoint = currentDragPoint;
[self autoscroll:theEvent];
[self setNeedsDisplay:YES]; //artifacts are left if this is off.
}
- (void)mouseUp:(NSEvent *)theEvent {
if ([EditorController EditorMode] == AddObjectMode) {
} else if ([EditorController EditorMode] == EditObjectMode) {
} else if ([EditorController EditorMode] == DeleteObjectMode) {
}
[self setNeedsDisplay:YES];
}
I could very well be missing something obvious, but I think I'm too close to the code to see the solution for what it is. Any help is greatly appreciated! Thanks!

Answer 1

I think you are misunderstanding the way drawRect: and its argument works:
The message drawRect: is sent by cocoa whenever your view or parts of it need to be redrawn. The CGRect argument is the bounding box of all updated areas for the current redraw. That means that you should not derive any positions of objects within your view from this rectangle. It is only passed to the method to allow for optimized drawing: if something is completely outside of this rectangle it does not need to be redrawn.
You should calculate all positions within your view from the views coordinate system: [self bounds]. This does not change each time drawRect: is performed and gives you an origin and size for the contents of the view.
There are a couple of other issues with your code (for instance, don't call setFrame: from within drawRect:) but I think you should first get the coordinates right and then look further into how to calculate pixel-aligned coordinates for your rectangles.

Answer 2

This code of yours looks rather more elaborate than it needs to be. Check out NSCenterScanRect(), and NSRectFillListWithColors(). Also, it's rather wasteful to create and discard paths in -drawRect:.