Graphics Context

The "canvas" into which an application draws. More...

Collaboration diagram for Graphics Context:

Classes
class	Pebble::GContext

Functions
void	graphics_context_set_stroke_color (GContext *ctx, GColor color)
void	graphics_context_set_fill_color (GContext *ctx, GColor color)
void	graphics_context_set_text_color (GContext *ctx, GColor color)
void	graphics_context_set_compositing_mode (GContext *ctx, GCompOp mode)
void	graphics_context_set_antialiased (GContext *ctx, bool enable)
void	graphics_context_set_stroke_width (GContext *ctx, uint8_t stroke_width)

Detailed Description

The "canvas" into which an application draws.

The Pebble OS graphics engine, inspired by several notable graphics systems, including Apple’s Quartz 2D and its predecessor QuickDraw, provides your app with a canvas into which to draw, namely, the graphics context. A graphics context is the target into which graphics functions can paint, using Pebble drawing routines (see Drawing Primitives, Drawing Paths and Drawing Text).

A graphics context holds a reference to the bitmap into which to paint. It also holds the current drawing state, like the current fill color, stroke color, clipping box, drawing box, compositing mode, and so on. The GContext struct is the type representing the graphics context.

For drawing in your Pebble watchface or watchapp, you won't need to create a GContext yourself. In most cases, it is provided by Pebble OS as an argument passed into a render callback (the .update_proc of a Layer).

Your app can’t call drawing functions at any given point in time: Pebble OS will request your app to render. Typically, your app will be calling out to graphics functions in the .update_proc callback of a Layer.

See also

Layers

Drawing Primitives

Drawing Paths

Drawing Text

Function Documentation

graphics_context_set_antialiased()

void graphics_context_set_antialiased	(	GContext *	ctx,
		bool	enable
	)

Sets whether antialiasing is applied to stroke drawing

Parameters

ctx	The graphics context onto which to set the antialiasing
enable	True = antialiasing enabled, False = antialiasing disabled

Note

Default value is true.

graphics_context_set_compositing_mode()

void graphics_context_set_compositing_mode	(	GContext *	ctx,
		GCompOp	mode
	)

Sets the current bitmap compositing mode of the graphics context.

Parameters

ctx	The graphics context onto which to set the compositing mode
mode	The new compositing mode

See also

GCompOp

bitmap_layer_set_compositing_mode()

Note

At the moment, this only affects the bitmaps drawing operations – graphics_draw_bitmap_in_rect(), graphics_draw_rotated_bitmap, and anything that uses those APIs –, but it currently does not affect the filling or stroking operations.

graphics_context_set_fill_color()

void graphics_context_set_fill_color	(	GContext *	ctx,
		GColor	color
	)

Sets the current fill color of the graphics context.

Parameters

ctx	The graphics context onto which to set the fill color
color	The new fill color

graphics_context_set_stroke_color()

void graphics_context_set_stroke_color	(	GContext *	ctx,
		GColor	color
	)

Sets the current stroke color of the graphics context.

Parameters

ctx	The graphics context onto which to set the stroke color
color	The new stroke color

graphics_context_set_stroke_width()

void graphics_context_set_stroke_width	(	GContext *	ctx,
		uint8_t	stroke_width
	)

Sets the width of the stroke for drawing routines

Parameters

ctx	The graphics context onto which to set the stroke width
stroke_width	Width in pixels of the stroke.

Note

If stroke width of zero is passed, it will be ignored and will not change the value stored in GContext. Currently, only odd stroke_width values are supported. If an even value is passed in, the value will be stored as is, but the drawing routines will round down to the previous integral value when drawing. Default value is 1.

graphics_context_set_text_color()

void graphics_context_set_text_color	(	GContext *	ctx,
		GColor	color
	)

Sets the current text color of the graphics context.

Parameters

ctx	The graphics context onto which to set the text color
color	The new text color