Node2D Class

The Node2D class is a helper class which is useful for display devices which allocate their memory as a single rectangle of memory. In such devices, the stride of Blts is a constant regardless of the width of the actual surface. Many devices such as the S3Trio64 used in our sample use the current screen width as the width of the video memory and all Blts are assumed to have the same stride (or pitch) as the screen and the same pixel format.

For devices such as this, and in any place where you wish to allocate memory from a rectangular block of memory, the Node2D class can be used as follows:

Initialize the allocator by creating an initial Node2D object using the height, and width of the block - you may enter the width either in pixels or bytes however you should be aware that queries to allocated sub-rectangles of memory will return the origin of the allocated memory using the same units with which the original Node2D is created, and that suballocations must be done in the same units also.

Allocate sub-rectangles using the Alloc method of the root node. Examine the origin of the new node using the Top and Left method of the node. Finally the node may be freed using the Free() method:

// Assume we have a 640 pixel x 1000 line 
// block of memory starting at memBase
// to be allocated rectangularly
#define MEM_WIDTH_IN_PIXELS 640
#define PIXEL_BYTES 2
#define MEM_HEIGHT 1000
extern unsigned char *memBase;
Node2D AllMem(MEM_WIDTH_IN_PIXELS, MEM_HEIGHT);
// allocations will be done in pixels
// create a 20 x 40 surface
Node2D *pSurf1 = AllMem->Alloc( 20, 40 );
// Check that pSurf1 is not null!
// create a 100 x 100 surf
Node2D *pSurf2 = AllMem->Alloc( 100, 100 );
// Check that pSurf2 is not null!
int strideInBytes = MEM_WIDTH_IN_PIXELS * PIXEL_BYTES;
// Create a pointer the the top left of the block of
//    memory in surf1
unsigned char *ptr1 = memBase + strideInBytes * pSurf1->Top()
+ PIXEL_BYTES * pSurf1->Left();
// Now delete the surface(s)
pSurf1->Free();
pSurf2->free();