github.com/ajstarks/openvg

Testbed for exploring OpenVG on the Raspberry Pi.

First program

Here is the graphics equivalent of "hello, world"

// first OpenVG program
// Anthony Starks ([e-mail])
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include "VG/openvg.h"
#include "VG/vgu.h"
#include "fontinfo.h"
#include "shapes.h"

int main() {
	int width, height;
	char s[3];

	init(&width, &height);					// Graphics initialization

	Start(width, height);					// Start the picture
	Background(0, 0, 0);					// Black background
	Fill(44, 77, 232, 1);					// Big blue marble
	Circle(width / 2, 0, width);			// The "world"
	Fill(255, 255, 255, 1);					// White text
	TextMid(width / 2, height / 2, "hello, world", SerifTypeface, width / 10);	// Greetings 
	End();						   			// End the picture

	fgets(s, 2, stdin);				   		// look at the pic, end with [RETURN]
	finish();					            // Graphics cleanup
	exit(0);
}

API

Coordinates are VGfloat values, with the origin at the lower left, with x increasing to the right, and y increasing up. OpenVG specifies colors as a VGfloat array containing red, green, blue, alpha values ranging from 0.0 to 1.0, but typically colors are specified as RGBA (0-255 for RGB, A from 0.0 to 1.0)

Window (canvas) functions

void WindowClear() 

WindowClear clears the window to previously set background colour

void AreaClear(unsigned int x, unsigned int y, unsigned int w, unsigned int h)

AreaClear clears a given rectangle in window coordinates

void WindowOpacity(unsigned int a)

WindowOpacity sets the window opacity

void WindowPosition(int x, int y)

WindowPosition moves the window to given position

Setup and shutdown

void init(int *w, int *h)

Initialize the graphics: width and height of the canvas are returned. This should begin every program.

void initWindowSize(int x, int y, unsigned int w, unsigned int h)

Initialize with specific dimensions

void finish() 

Shutdown the graphics. This should end every program.

void Start(int width, int height)

Begin the picture, clear the screen with a default white, set the stroke and fill to black.

void End()

End the picture, rendering to the screen.

void SaveEnd(char *filename)

End the picture, rendering to the screen, save the raster to the named file as 4-byte RGBA words, with a stride of width*4 bytes. The program raw2png converts the "raw" raster to png.

void saveterm(), restoreterm(), rawterm()

Terminal settings, save current settings, restore settings, put the terminal in raw mode.

Attributes

void setfill(float color[4])

Set the fill color

void Background(unsigned int r, unsigned int g, unsigned int b)

Fill the screen with the background color defined from RGB values.

void BackgroundRGB(unsigned int r, unsigned int g, unsigned int b, VGfloat a)

clears the screen to a background color with alpha

void StrokeWidth(float width)

Set the stroke width.

void RGBA(unsigned int r, unsigned int g, unsigned int b, VGfloat a, VGfloat color[4])

fill a color vector from RGBA values.

void RGB(unsigned int r, unsigned int g, unsigned int b, VGfloat color[4])

fill a color vector from RGB values.

void Stroke(unsigned int r, unsigned int g, unsigned int b, VGfloat a)

Set the Stroke color using RGBA values.

void Fill(unsigned int r, unsigned int g, unsigned int b, VGfloat a)

Set the Fill color using RGBA values.

void FillLinearGradient(VGfloat x1, VGfloat y1, VGfloat x2, VGfloat y2, VGfloat *stops, int n)

Set the fill to a linear gradient bounded by (x1, y1) and (x2, y2). using offsets and colors specified in n number of stops

void FillRadialGradient(VGfloat cx, VGfloat cy, VGfloat fx VGfloat fy, VGfloat r, VGfloat *stops, int n)

Set the fill to a radial gradient centered at (cx, cy) with radius r, and focal point at (fx, ry), using offsets and colors specified in n number of stops

Shapes

void Line(VGfloat x1, VGfloat y1, VGfloat x2, VGfloat y2)

Draw a line between (x1, y1) and (x2, y2).

void Rect(VGfloat x, VGfloat y, VGfloat w, VGfloat h)

Draw a rectangle with its origin (lower left) at (x,y), and size is (width,height).

void RectOutline(VGfloat x, VGfloat y, VGfloat w, VGfloat h)

Outlined version

void Roundrect(VGfloat x, VGfloat y, VGfloat w, VGfloat h, VGfloat rw, VGfloat rh)

Draw a rounded rectangle with its origin (lower left) at (x,y), and size is (width,height).
The width and height of the corners are specified with (rw,rh).

void RoundrectOutline(VGfloat x, VGfloat y, VGfloat w, VGfloat h, VGfloat rw, VGfloat rh)

Outlined version

void Polygon(VGfloat *x, VGfloat *y, VGint n)

Draw a polygon using the coordinates in arrays pointed to by x and y. The number of coordinates is n.

void Polyline(VGfloat *x, VGfloat *y, VGint n)

Draw a polyline using the coordinates in arrays pointed to by x and y. The number of coordinates is n.

void Circle(VGfloat x, VGfloat y, VGfloat d)

Draw a circle centered at (x,y) with diameter d.

void CircleOutline(VGfloat x, VGfloat y, VGfloat r)

Outlined version

void Ellipse(VGfloat x, VGfloat y, VGfloat w, VGfloat h)

Draw an ellipse centered at (x,y) with radii (w, h).

void EllipseOutline(VGfloat x, VGfloat y, VGfloat w, VGfloat h)

Outlined version

void Qbezier(VGfloat sx, VGfloat sy, VGfloat cx, VGfloat cy, VGfloat ex, VGfloat ey)

Draw a quadratic bezier curve beginning at (sx, sy), using control points at (cx, cy), ending at (ex, ey).

void QbezierOutline(VGfloat sx, VGfloat sy, VGfloat cx, VGfloat cy, VGfloat ex, VGfloat ey)

Outlined version

void Cbezier(VGfloat sx, VGfloat sy, VGfloat cx, VGfloat cy, VGfloat px, VGfloat py, VGfloat ex, VGfloat ey)

Draw a cubic bezier curve beginning at (sx, sy), using control points at (cx, cy) and (px, py), ending at (ex, ey).

void CbezierOutline(VGfloat sx, VGfloat sy, VGfloat cx, VGfloat cy, VGfloat px, VGfloat py, VGfloat ex, VGfloat ey) 

Outlined version

void Arc(VGfloat x, VGfloat y, VGfloat w, VGfloat h, VGfloat sa, VGfloat aext)

Draw an elliptical arc centered at (x, y), with width and height at (w, h). Start angle (degrees) is sa, angle extent is aext.

void ArcOutline(VGfloat x, VGfloat y, VGfloat w, VGfloat h, VGfloat sa, VGfloat aext)

Outlined version

Text and Images

void Text(VGfloat x, VGfloat y, char* s, Fontinfo f, int pointsize)

Draw a the text srtring (s) at location (x,y), using pointsize.

void TextMid(VGfloat x, VGfloat y, char* s, Fontinfo f, int pointsize)

Draw a the text srtring (s) at centered at location (x,y), using pointsize.

void TextEnd(VGfloat x, VGfloat y, char* s, Fontinfo f, int pointsize)

Draw a the text srtring (s) at with its lend aligned to location (x,y), using pointsize

VGfloat TextWidth(char *s, Fontinfo f, int pointsize)

Return the width of text

VGfloat TextHeight(Fontinfo f, int pointsize)

Return a font's height

TextDepth(Fontinfo f, int pointsize)

Return a font's distance beyond the baseline.

void Image(VGfloat x, VGfloat y, int w, int h, char * filename)

place a JPEG image with dimensions (w,h) at (x,y).

Transformations

void Translate(VGfloat x, VGfloat y)

Translate the coordinate system to (x,y).

void Rotate(VGfloat r)

Rotate the coordinate system around angle r (degrees).

void Scale(VGfloat x, VGfloat y)

Scale by x,y.

void Shear(VGfloat x, VGfloat y)

Shear by the angles x,y.

Clipping

void ClipRect(VGint x, VGint y, VGint w, VGint h)

Limit drawing the drawing area to the specified rectangle, end with ClipEnd()

void ClipEnd()

Ends clipping area

Using fonts

Also included is the font2openvg program, which turns font information into C source that you can embed in your program. The Makefile makes font code from files found in /usr/share/fonts/truetype/ttf-dejavu/. If you want to use other fonts, adjust the Makefile accordingly, or generate the font code on your own once the font2openvg program is built.

font2openvg takes three arguments: the TrueType font file, the output file to be included and the prefix for identifiers. For example to use the DejaVu Sans font:

./font2openvg /usr/share/fonts/truetype/ttf-dejavu/DejaVuSans.ttf DejaVuSans.inc DejaVuSans

and include the generated code in your program:

#include "DejaVuSans.inc"
Fontinfo DejaFont

The loadfont function creates OpenVG paths from the font data:

loadfont(DejaVuSans_glyphPoints, 
        DejaVuSans_glyphPointIndices, 
    	DejaVuSans_glyphInstructions,                
    	DejaVuSans_glyphInstructionIndices, 
        DejaVuSans_glyphInstructionCounts, 
        DejaVuSans_glyphAdvances,
        DejaVuSans_characterMap, 
    	DejaVuSans_glyphCount);

The unloadfont function releases the path information:

unloadfont(DejaFont.Glyphs, DejaFont.Count);

Note that the location of the font files may differ. (The current location for Jessie is /usr/share/fonts/truetype/ttf-dejavu) Use the FONTLIB makefile variable to adjust this location.

Build and run

Note that you will need at least 64 Mbytes of GPU RAM:. You will also need the DejaVu fonts, and the jpeg and freetype libraries. The indent tool is also useful for code formatting. Install them via:

pi@raspberrypi ~ $ sudo apt-get install libjpeg8-dev indent libfreetype6-dev ttf-dejavu-core

Next, build the library and test:

pi@raspberrypi ~ $ git clone git://github.com/ajstarks/openvg
pi@raspberrypi ~ $ cd openvg
pi@raspberrypi ~/openvg $ make
g++ -I/usr/include/freetype2 fontutil/font2openvg.cpp -o font2openvg -lfreetype
./font2openvg /usr/share/fonts/truetype/ttf-dejavu/DejaVuSans.ttf DejaVuSans.inc DejaVuSans
224 glyphs written
./font2openvg /usr/share/fonts/truetype/ttf-dejavu/DejaVuSansMono.ttf DejaVuSansMono.inc DejaVuSansMono
224 glyphs written
./font2openvg /usr/share/fonts/truetype/ttf-dejavu/DejaVuSerif.ttf DejaVuSerif.inc DejaVuSerif
224 glyphs written
gcc -O2 -Wall -I/opt/vc/include -I/opt/vc/include/interface/vmcs_host/linux -I/opt/vc/include/interface/vcos/pthreads -c libshapes.c
gcc -O2 -Wall -I/opt/vc/include -I/opt/vc/include/interface/vmcs_host/linux -I/opt/vc/include/interface/vcos/pthreads -c oglinit.c
pi@raspberrypi ~/openvg/client $ cd client
pi@raspberrypi ~/openvg/client $ make test
cc -Wall -I/opt/vc/include -I/opt/vc/include/interface/vcos/pthreads -o shapedemo shapedemo.c ../libshapes.o ../oglinit.o -L/opt/vc/lib -lGLESv2 -ljpeg
./shapedemo demo 5

The program "shapedemo" exercises a high-level API built on OpenVG found in libshapes.c.

./shapedemo                      # show a reference card
./shapedemo raspi                # show a self-portrait
./shapedemo image                # show four test images
./shapedemo astro                # the sun and the earth, to scale
./shapedemo text                 # show blocks of text in serif, sans, and mono fonts
./shapedemo rand 10              # show 10 random shapes
./shapedemo rotate 10 a          # rotated and faded "a"
./shapedemo test "hello, world"  # show a test pattern, with "hello, world" at mid-display in sans, serif, and mono.
./shapedemo fontsize             # show a range of font sizes (per <https://speakerdeck.com/u/idangazit/p/better-products-through-typography>)
./shapedemo demo 10              # run through the demo, pausing 10 seconds between each one; contemplate the awesome.

To install the shapes library as a system-wide shared library

pi@raspberrypi ~/openvg $ make library
pi@raspberrypi ~/openvg $ sudo make install

The openvg shapes library can now be used in C code by including shapes.h and fontinfo.h and linking with libshapes.so:

#include <shapes.h>
#include <fontinfo.h>

pi@raspberrypi ~ $ gcc -I/opt/vc/include -I/opt/vc/include/interface/vmcs_host/linux -I/opt/vc/include/interface/vcos/pthreads anysource.c -o anysource -lshapes
pi@raspberrypi ~ $ ./anysource

Go wrapper

A Go programming language wrapper for the library is found in openvg.go. Sample clients are in the directory go-client. The API closely follows the C API; here is the "hello, world" program in Go:

The Go API

package main

import (
	"bufio"
	"github.com/ajstarks/openvg"
	"os"
)

func main() {
	width, height := openvg.Init() // OpenGL, etc initialization

	w2 := openvg.VGfloat(width / 2)
	h2 := openvg.VGfloat(height / 2)
	w := openvg.VGfloat(width)

	openvg.Start(width, height)                               // Start the picture
	openvg.BackgroundColor("black")                           // Black background
	openvg.FillRGB(44, 77, 232, 1)                            // Big blue marble
	openvg.Circle(w2, 0, w)                                   // The "world"
	openvg.FillColor("white")                                 // White text
	openvg.TextMid(w2, h2, "hello, world", "serif", width/10) // Greetings 
	openvg.End()                                              // End the picture
	bufio.NewReader(os.Stdin).ReadBytes('\n')                 // Pause until [RETURN]
	openvg.Finish()                                           // Graphics cleanup
}

To build the wrapper: (make sure GOPATH is set)

pi@raspberrypi ~/openvg $ go install .
pi@raspberrypi ~/openvg $ cd go-client/hellovg
pi@raspberrypi ~/openvg/go-client/hellovg $ go build .
pi@raspberrypi ~/openvg/go-client/hellovg $ ./hellovg