How to do ‘page-flipping’ The steps needed when revising our ‘wfmodel1.cpp’ prototype to achieve ‘smooth’ animation

How page-flipping works VRAM The ‘visible’ page The ‘drawing’ page CRTC START-ADDRESS The user sees this part of video memory Your program draws to this part of video memory When the ‘drawing’ page is ready to be viewed, your program changes the CRTC START-ADDRESS and thus the roles of these two pages are ‘flipped’

Use a Radeon-specific register The CRT Controller’s Start-Address can be accessed via a 32-bit register (called CRTC_START) which is part of the ATI Radeon’s 2D drawing engine -- allowing the Start-Address to be reprogrammed as a single atomic operation #define CRTC_START 0x0224

Installation check The software must detect the presence of a Radeon X300 graphics adapter, and it must discover which i/o port-address got assigned to the Radeon 2D engine during the Operating System’s startup process #define VENDOR_ID 0x1002// ATI #define DEVICE_ID 0x5B60// X300

PCI Find Device service init8086(); // initialization for vm8086 vm.regs.eax = 0x1B02; // PCI Find Device vm.regs.ecx = DEVICE_ID; // X300 vm.regs.edx = VENDOR_ID; // ATI vm.regs.esi = 0;// device index int86( 0x1A, vm );// invoke PCI BIOS if ( vm.regs.eax & 0xFF00 ) exit(1); // failed

PCI Read Configuration Dword vm.regs.eax = 0x1B0A; // PCI Read Dwd vm.regs.edi = 0x0014; // Resource #1 Adr int86( 0x1A, vm );// invoke PCI BIOS iobase = vm.regs.ecx & 0xFFFFFFFC;

Global Variables intiobase; // value is filled in at runtime intpage_size = (2 << 20); // 2-megabytes intdrawing_page = 0;// page 0 or page 1 intvisible_page = 0;// page 0 or page 1

Hardware helper-function void set_visible_page( void ) { intstart_addr = visible_page * page_size; outl( CRTC_START, iobase + 0 ); outl( start_addr, iobase + 4 ); }

Pixel-drawing helper-function void draw_pixel( int x, int y, int color ) { int offset = drawing_page * page+size; unsigned char *dstn = vram + offset; dstn[ y * vres + x ] = color; }

The ‘page-flipping’ algorithm Main loop: –Compute the new image –Set drawing_page to (visible_page + 1)%2 –Draw next screen image onto drawing page –Set visible_page to equal the drawing_page

In-class exercise Create a revision of the ‘wfmodel2’ demo (named ‘wfmodel3.cpp’) to automatically spin the wireframe model contiunuously, until the user hits the -key You will need to use a signal-handler and asynchronous keyboard-input notification (as in our earlier ‘persists.cpp’ demo)