Drawing

Collaboration diagram for Drawing:

Functions
void	bj_draw_line (struct bj_bitmap *bitmap, int x0, int y0, int x1, int y1, uint32_t pixel)
void	bj_draw_rectangle (struct bj_bitmap *bitmap, const struct bj_rect *area, uint32_t pixel)
void	bj_draw_filled_rectangle (struct bj_bitmap *bitmap, const struct bj_rect *area, uint32_t pixel)
void	bj_draw_triangle (struct bj_bitmap *bitmap, int x0, int y0, int x1, int y1, int x2, int y2, uint32_t color)
void	bj_draw_filled_triangle (struct bj_bitmap *bitmap, int x0, int y0, int x1, int y1, int x2, int y2, uint32_t color)
void	bj_draw_circle (struct bj_bitmap *bitmap, int cx, int cy, int radius, uint32_t color)
void	bj_draw_filled_circle (struct bj_bitmap *bitmap, int cx, int cy, int radius, uint32_t color)
void	bj_draw_polyline (struct bj_bitmap *bitmap, size_t count, const int *x, const int *y, bj_bool loop, uint32_t color)

Detailed Description

Draw lines, shapes, and outlines into a bitmap.

These functions draw simple geometric shapes into a bj_bitmap. pixels, lines, rectangles, triangles, circles, and polylines (a series of connected line segments). Each function writes directly into the destination bitmap's pixels; there's no draw queue or scene graph. The pattern is:

1. Get a bitmap to draw into (commonly the window's framebuffer via bj_render_target_bitmap).
2. Pick a colour: build a uint32_t packed in the bitmap's pixel format with bj_make_bitmap_pixel.
3. Call as many drawing functions as you need; they modify the bitmap in place.
4. Push the bitmap to the screen with bj_invalidate_window.

static void on_draw(struct bj_window* w, struct bj_render_target* t,
                    const struct bj_rect* dirty, void* user_data) {
    bj_bitmap* fb  = bj_render_target_bitmap(t);
    uint32_t   red = bj_make_bitmap_pixel(fb, 0xFF, 0x00, 0x00);
 
    bj_clear_bitmap(fb);
    bj_draw_filled_circle(fb, 320, 240, 100, red);
    bj_draw_rectangle(fb, &(bj_rect){.x=10,.y=10,.w=64,.h=64}, red);
}
/* in setup: bj_set_draw_callback(window, on_draw, NULL);
   bj_invalidate_window(window); *‍/

Outlined or filled

Rectangles, triangles, and circles each come in two flavours: bj_draw_rectangle / bj_draw_filled_rectangle and so on. "Outlined" draws just the edge; "filled" colours every pixel inside. Lines and polylines are obviously line-only.

Bounds are your responsibility

Warning

These functions don't check that the coordinates you pass are inside the bitmap. If you ask to draw a circle at (10000, 10000) on a 640×480 bitmap, you'll corrupt memory or crash. The trade-off is speed: the drawing loop is one less conditional per pixel. If your code generates coordinates that might land outside the bitmap, clamp them yourself before calling.

See also

bj_clear_bitmap to wipe the destination first, drawing_2d.c for every primitive in one program, drawing_text.c for text rendering on top of these primitives.

Function Documentation

bj_draw_circle()

void bj_draw_circle	(	struct bj_bitmap *	bitmap,
		int	cx,
		int	cy,
		int	radius,
		uint32_t	color )

Draw the outline of a circle onto a bitmap.

Uses the midpoint circle algorithm (integer arithmetic).

Parameters

bitmap	Target bitmap (must not be NULL).
cx	X-coordinate of circle centre (pixels).
cy	Y-coordinate of circle centre (pixels).
radius	Circle radius in pixels (>= 0).
color	Pixel colour in 0xAARRGGBB format.

bj_draw_filled_circle()

void bj_draw_filled_circle	(	struct bj_bitmap *	bitmap,
		int	cx,
		int	cy,
		int	radius,
		uint32_t	color )

Draw a filled circle onto a bitmap.

Fills all pixels within radius distance from (cx, cy).

Parameters

bitmap	Target bitmap (must not be NULL).
cx	X-coordinate of circle centre (pixels).
cy	Y-coordinate of circle centre (pixels).
radius	Circle radius in pixels (>= 0).
color	Pixel colour in 0xAARRGGBB format.

Examples

drawing_2d.c, interpolation.c, physics_kinematics.c, physics_particle.c, pong.c, and start.c.

Referenced by draw(), draw(), draw(), draw(), on_draw(), and on_draw().

bj_draw_filled_rectangle()

void bj_draw_filled_rectangle	(	struct bj_bitmap *	bitmap,
		const struct bj_rect *	area,
		uint32_t	pixel )

Draws a filled rectangle in the given bitmap.

The function draws an filled rectangle by filling all pixels within area.

Parameters

bitmap	The bitmap object.
area	The rectangle to draw.
pixel	The line pixel value.

Memory Safety

This function does not perform any bound checking on the pixel coordinates. It is up to you to ensure the coordinates lie between [0, struct bj_bitmap->width * struct bj_bitmap->height]. Writing outside of these bounds will result in undefined behaviour or corrupted memory access.

Examples

bitmap_blit_colorkey.c, drawing_2d.c, pong.c, and random_distribution.c.

Referenced by draw(), draw(), and setup().

bj_draw_filled_triangle()

void bj_draw_filled_triangle	(	struct bj_bitmap *	bitmap,
		int	x0,
		int	y0,
		int	x1,
		int	y1,
		int	x2,
		int	y2,
		uint32_t	color )

Draws a filled triangle given its 3 corners.

Parameters

bitmap	The bitmap object.
x0	The X coordinate of the first triangle vertex.
y0	The Y coordinate of the first triangle vertex.
x1	The X coordinate of the second triangle vertex.
y1	The Y coordinate of the second triangle vertex.
x2	The X coordinate of the third triangle vertex.
y2	The Y coordinate of the third triangle vertex.
color	The fill colour.

Memory Safety

This function does not perform any bound checking on the pixel coordinates. It is up to you to ensure the coordinates lie between [0, struct bj_bitmap->width * struct bj_bitmap->height]. Writing outside of these bounds will result in undefined behaviour or corrupted memory access.

Examples

drawing_2d.c.

Referenced by draw().

bj_draw_line()

void bj_draw_line	(	struct bj_bitmap *	bitmap,
		int	x0,
		int	y0,
		int	x1,
		int	y1,
		uint32_t	pixel )

Draws a line of pixels in the given bitmap.

The line is drawn for each pixel between p0 and p1.

Parameters

bitmap	The bitmap object.
x0	The X coordinate of the first point in the line.
y0	The Y coordinate of the first point in the line.
x1	The X coordinate of the second point in the line.
y1	The Y coordinate of the second point in the line.
pixel	The line pixel value.

Memory Safety

This function does not perform any bound checking on the pixel coordinates. It is up to you to ensure the coordinates lie between [0, struct bj_bitmap->width * struct bj_bitmap->height]. Writing outside of these bounds will result in undefined behaviour or corrupted memory access.

Examples

random_distribution.c.

Referenced by draw().

bj_draw_polyline()

void bj_draw_polyline	(	struct bj_bitmap *	bitmap,
		size_t	count,
		const int *	x,
		const int *	y,
		bj_bool	loop,
		uint32_t	color )

Draw a polyline from C-style coordinate arrays.

Draws line segments between successive vertex pairs (x[i], y[i]) -> (x[i+1], y[i+1]). If loop != 0 and count >= 2, an extra segment connects the last vertex to the first.

Parameters

bitmap	Target bitmap.
x	Pointer to array of x coordinates (length >= count).
y	Pointer to array of y coordinates (length >= count).
count	Number of vertices. Segments drawn for i = 0..count-2.
color	Pixel colour in 0xAARRGGBB format.
loop	Nonzero to close the polyline.

Examples

drawing_2d.c.

Referenced by draw().

bj_draw_rectangle()

void bj_draw_rectangle	(	struct bj_bitmap *	bitmap,
		const struct bj_rect *	area,
		uint32_t	pixel )

Draws a rectangle in the given bitmap.

The function draws an rectangle outline using 4 consecutive calls to bj_draw_line.

Parameters

bitmap	The bitmap object.
area	The rectangle to draw.
pixel	The line pixel value.

Memory Safety

This function does not perform any bound checking on the pixel coordinates. It is up to you to ensure the coordinates lie between [0, struct bj_bitmap->width * struct bj_bitmap->height]. Writing outside of these bounds will result in undefined behaviour or corrupted memory access.

Examples

drawing_2d.c, random_distribution.c, and start.c.

Referenced by draw(), and on_draw().

bj_draw_triangle()

void bj_draw_triangle	(	struct bj_bitmap *	bitmap,
		int	x0,
		int	y0,
		int	x1,
		int	y1,
		int	x2,
		int	y2,
		uint32_t	color )

Draws the edges of a triangle given its 3 corners.

Parameters

bitmap	The bitmap object.
x0	The X coordinate of the first triangle vertex.
y0	The Y coordinate of the first triangle vertex.
x1	The X coordinate of the second triangle vertex.
y1	The Y coordinate of the second triangle vertex.
x2	The X coordinate of the third triangle vertex.
y2	The Y coordinate of the third triangle vertex.
color	The line colour.

Memory Safety

This function does not perform any bound checking on the pixel coordinates. It is up to you to ensure the coordinates lie between [0, struct bj_bitmap->width * struct bj_bitmap->height]. Writing outside of these bounds will result in undefined behaviour or corrupted memory access.

Examples

drawing_2d.c.

Referenced by draw().