Graphics Primitives

MoSync provides a number of primitive graphics operations at the syscall level.

 int maSetColor (int rgb); 
 void maSetClipRect (int left, int top, int width, int height); 
 void maGetClipRect (MARect *out); 
 void maPlot (int posX, int posY); 
 void maLine (int startX, int startY, int endX, int endY); 
 void maFillRect (int left, int top, int width, int height); 
 void maFillTriangleStrip (const MAPoint2d *points, int count); 
 void maFillTriangleFan (const MAPoint2d *points, int count); 
 void maDrawText (int left, int top, const char *str); 

The maSetColor() function sets a "current color" which will be used by any subsequent primitive operations. The maSetClipRect() and maGetClipRect() functions are used to either define or query a rectangular area of the screen that is affected by graphics operations. The rest of the functions each draw a primitive. All functions deal with coordinates in one way or another, and these coordinates are pixels coordinates with the origin located at the top-left corner of the screen. The positive x axis goes from left to right, while the positive y axis goes from top to bottom:

Plotting Pixels

The maPlot() function is used to plot individual pixels at given coordinates using the current color:

// Set the current color to a bright green.
maSetColor(0x00ff00); 

// plot a pixel at 10, 10.
maPlot(10, 10); 

// Update the screen.
maUpdateScreen(); 

// set the current color to a bright green.
maSetColor(0x00ff00); 

// draw a line from (10,10) to (50, 50).
maLine(10, 10, 50, 50); 

// update the screen.
maUpdateScreen(); 

// set the current color to a bright green.
maSetColor(0x00ff00); 

// draw a rectangle between (10, 10) and (60, 60).
maFillRect(10, 10, 50, 50);

// update the screen.
maUpdateScreen(); 

// Set the current color to a bright green.
maSetColor(0x00ff00); 
MAPoint2d points[] = 
{ 
    {10, 10}, {40, 10}, {10, 40}, {40, 40} 
};

maFillTriangleStrip(points, 4);

// Update the screen.
maUpdateScreen();

A triangle fan is a primitive in computer graphics that saves on storage and processing time. It describes a set of connected triangles that share one central vertex. If N is the number of triangles in the fan, the number of vertices describing it is N+2. This is a considerable improvement over the 3N vertices that are necessary to describe the triangles separately:

MAPoint2d points[8]; 
points[0].x = points[0].y = 40; 
points[7].x = points[7].y = 40; 
for(int i = 0; i < 7; i++) 
{ 
    float t = 2*M_PI*i / 6.0; 
    points[i+1].x = 40 + 30*cos(t); 
    points[i+1].y = 40 + 30*sin(t); 
} 
maSetColor(0xff00ff); 
maFillTriangleFan(points, 8); 
maUpdateScreen(); 

Drawing Text

The maDrawText() function is used to render text using a device-dependent font. It is useful for things like debug printouts or simplier UI:s. For consistent, flexible fonts, have a look at the MAUtil::Font class - see Font tools.

// set the current color to a bright green.
maSetColor(0x00ff00); 
maDrawText(10, 10, "Hello world!");

// update the screen.
maUpdateScreen();