Graphics Bitmaps Drawing alphabetic characters and multicolor patterns Finding the ROM fonts Standard BIOS service locates ROM fonts Designed to execute in 8086 real mode Normal service call protocol is followed Parameters are placed in CPU registers Software interrupt instruction is executed ROM BIOS code performs desired service Parameters may be returned in registers Example AT T assembly language syntax mov 0x11 ah char gen services mov 0x30 al get font information mov 2 bh 8x14 font address int 0x10 request BIOS service the font address is returned in ES BP and count of scanlines should be in CX Interface for Linux No C syntax to access CPU registers Software interrupt is privileged operation Must call kernel to obtain BIOS services How to do it isn t very clearly documented SVGALIB Project includes LRMI wrapper An acronym for Linux Real Mode Interface Idea make it easy to invoke BIOS calls How LRMI is used C program needs include lrmi h Needs to do initialization LRMI init Declares struct LRMI regs reg 0 Code example reg eax 0x1130 reg ebx 0x0200 LRMI int 0x10 reg int font address reg ebp 16 reg es Link with lrmi o object module Need to precompile lrmi c source text gcc c lrmi c For C you need overriding prototypes extern C int LRMI init void etc include lrmi h this comes after To compile and link your C program g drawtext cpp lrmi o o drawtext Acknowledgement The author of LRMI is Josh Vanderhoof His code is part of the SVGALIB package Full package can be downloaded from http www svgalib org Downloaded as a compressed tar file Example svgalib 1 4 3 tar gz Use the tar command to expand it tar xvzf svgalib 1 4 3 tar gz Copying 8x14 ROM font Need to memory map the ROM region mmap requires map to be 4K aligned Size of mapped region 0x1000 256 16 Need to allocate a local array in RAM static unsigned char glyph 256 16 for c 0 c 256 c for r 0 r 14 r glyph c r font addr Drawing a character in mode 19 Must memory map the VRAM window Physical base address is 0x000A0000 Size of VRAM window is 64K 64 10 Use the ascii code as a glyph table index Specify the character s foreground color Use x y coordinates for character location So your function prototype could be void draw char int ascii int color Implementing draw char int hres 320 vres 200 unsigned char dstn 0x000A0000 dstn y hres x where to start drawing for r 0 r 14 r 14 rows high for w 0 w 8 w 8 pixels wide if glyph ascii r 0x80 w dstn w fgcolor dstn hres drop to next screen row Some comparisons text mode character generator imposes a fixed grid All characters from a common glyph table Character backgrounds always solid color graphics mode You can freely mix numerous font styles You can place characters at any positions You can draw against backgound patterns Using bitmap patterns You can create interesting backgrounds Fill screen regions with a copied pattern 0xFF 0x80 0x80 0x80 0xFF 0x08 0x08 0x08 foreground color background color Algorithm for tiling mode 19 unsigned char pat 8 8x8 2 color bitmap unsigned char vram 0x000A0000 color for int y 0 y vres v for int x 0 x hres x int r y 8 k x 8 color pat r 0x80 k fg bg vram y hres x color Automating pattern creation Try these standard runtime functions include stdlib h int rand void void srand unsigned int seed Can make new 8x8 patterns like this for k 0 k 8 k pat k rand fgcolor rand bgcolor rand Esthetics Use a brighter color in the foreground Use a darker color in the background To implement this discipline we need to know how the color table is arranged In mode 19 there are 256 default colors Among these are 24 color groups 3 intensity levels plus 3 saturation levels The default colors mode 19 Range for the 72 brightest colors 32 103 Range for the 72 midlevel colors 104 175 Range for the 72 darkest colors 176 247 Colors 0 15 are the standard EGA colors Colors 16 31 are sixteen grayscale colors Colors 248 255 are solid black default But all of these are fully programmable Choosing a random color pair foreground color from the bright range fgcolor rand 0xFF 72 32 Background color from the dark range bgcolor rand 0xFF 72 104 Using patterns with more colors Same concepts can be extended But need a larger pattern bitmap Example use 2 bits per pixel 4 colors An 8x8 pattern that using 4 colors unsigned short pat2bpp 8 unsigned char palette4 4 for r 0 r 8 r pat2bpp r rand for c 0 c 4 c palette4 c rand Tiling with a 4 color bitmap for y 0 y hres y unsigned short bits pat2bpp y 8 for x 0 x hres x int i bits x 8 3 int color palette4 i vram y hres x color Automating an art show Can use a standard C runtime function include stdlib h void sleep int seconds User views your screen for fixed duration while done draw next scene sleep 1
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