Set up slidier widths properly.

redo/reredo/darwin/slider.m

@@ -1,6 +1,26 @@
 // 14 august 2015
 #import "uipriv_darwin.h"
 
+// Horizontal sliders have no intrinsic width; we'll use the default Interface Builder width for them.
+// This will also be used for the initial frame size, to ensure the slider is always horizontal (see below).
+#define sliderWidth 92
+
+@interface libui_intrinsicWidthNSSlider : NSSlider
+@end
+
+@implementation libui_intrinsicWidthNSSlider
+
+- (NSSize)intrinsicContentSize
+{
+	NSSize s;
+
+	s = [super intrinsicContentSize];
+	s.width = sliderWidth;
+	return s;
+}
+
+@end
+
 struct uiSlider {
 	uiDarwinControl c;
 	NSSlider *slider;
@@ -95,8 +115,10 @@ uiSlider *uiNewSlider(intmax_t min, intmax_t max)
 
 	s = (uiSlider *) uiNewControl(uiSliderType());
 
-	s->slider = [[NSSlider alloc] initWithFrame:NSZeroRect];
-	// TODO vertical is defined by wider than tall
+	// a horizontal slider is defined as one where the width > height, not by a flag
+	// to be safe, don't use NSZeroRect, but make it horizontal from the get-go
+	s->slider = [[libui_intrinsicWidthNSSlider alloc]
+		initWithFrame:NSMakeRect(0, 0, sliderWidth, 2)];
 	[s->slider setMinValue:min];
 	[s->slider setMaxValue:max];
 	[s->slider setAllowsTickMarkValuesOnly:NO];