5 * (C)1993 Ztiff Zox Softwear
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7 * Simple graphics library to accompany the article
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9 * INTRODUCTION TO MODE X.
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11 * This library provides the basic functions for initializing and using
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12 * unchained (planar) 256-color VGA modes. Currently supported are:
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17 * Functions are provided for:
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19 * - initializing one of the available modes
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20 * - setting the start address of the VGA refresh data
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21 * - setting active and visible display pages
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22 * - writing and reading a single pixel to/from video memory
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24 * The library is provided as a demonstration only, and is not claimed
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25 * to be particularly efficient or suited for any purpose. It has only
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26 * been tested with Borland C++ 3.1 by the author. Comments on success
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27 * or disaster with other compilers are welcome.
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29 * This file is public domain. Do with it whatever you'd like, but
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30 * please don't distribute it without the article.
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32 * Thanks go out to various helpful netters who spotted the 0xE7 bug
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33 * in the set320x240x256() function!
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35 * modified by sparky4 so it can be compiled in open watcom ^^
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40 * We 'require' a large data model simply to get rid of explicit 'far'
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41 * pointers and compiler specific '_fmemset()' functions and the likes.
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44 #if !defined(__COMPACT__)
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45 # if !defined(__LARGE__)
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46 # if !defined(__HUGE__)
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47 # error Large data model required! Try compiling with 'bcc -ml lib.c'.
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57 * Comment out the following #define if you don't want the testing main()
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64 * Define the port addresses of some VGA registers.
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67 #define CRTC_ADDR 0x3d4 /* Base port of the CRT Controller (color) */
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69 #define SEQU_ADDR 0x3c4 /* Base port of the Sequencer */
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70 #define GRAC_ADDR 0x3ce /* Base port of the Graphics Controller */
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74 * Make a far pointer to the VGA graphics buffer segment. Your compiler
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75 * might not have the MK_FP macro, but you'll figure something out.
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78 typedef unsigned char UCHAR;
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79 UCHAR *vga = (UCHAR *) MK_FP(0xA000, 0);
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82 * width and height should specify the mode dimensions. widthBytes
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83 * specify the width of a line in addressable bytes.
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86 unsigned width, height, widthBytes;
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89 * actStart specifies the start of the page being accessed by
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90 * drawing operations. visStart specifies the contents of the Screen
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91 * Start register, i.e. the start of the visible page.
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94 unsigned actStart, visStart;
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97 * set320x200x256_X()
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98 * sets mode 13h, then turns it into an unchained (planar), 4-page
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102 void set320x200x256_X(void)
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107 /* Set VGA BIOS mode 13h: */
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110 int86(0x10, &r, &r);
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112 /* Turn off the Chain-4 bit (bit 3 at index 4, port 0x3c4): */
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114 outpw(SEQU_ADDR, 0x0604);
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116 /* Turn off word mode, by setting the Mode Control register
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117 of the CRT Controller (index 0x17, port 0x3d4): */
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119 outpw(CRTC_ADDR, 0xE317);
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121 /* Turn off doubleword mode, by setting the Underline Location
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122 register (index 0x14, port 0x3d4): */
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124 outpw(CRTC_ADDR, 0x0014);
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126 /* Clear entire video memory, by selecting all four planes, then
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127 writing 0 to entire segment. */
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129 outpw(SEQU_ADDR, 0x0F02);
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130 memset(vga+1, 0, 0xffff); /* stupid size_t exactly 1 too small */
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133 /* Update the global variables to reflect dimensions of this
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134 mode. This is needed by most future drawing operations. */
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139 /* Each byte addresses four pixels, so the width of a scan line
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140 in *bytes* is one fourth of the number of pixels on a line. */
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142 widthBytes = width / 4;
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144 /* By default we want screen refreshing and drawing operations
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145 to be based at offset 0 in the video segment. */
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147 actStart = visStart = 0;
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152 * setActiveStart() tells our graphics operations which address in video
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153 * memory should be considered the top left corner.
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156 void setActiveStart(unsigned offset)
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162 * setVisibleStart() tells the VGA from which byte to fetch the first
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163 * pixel when starting refresh at the top of the screen. This version
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164 * won't look very well in time critical situations (games for
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165 * instance) as the register outputs are not synchronized with the
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166 * screen refresh. This refresh might start when the high byte is
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167 * set, but before the low byte is set, which produces a bad flicker.
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170 void setVisibleStart(unsigned offset)
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173 outpw(CRTC_ADDR, 0x0C); /* set high byte */
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174 outpw(CRTC_ADDR+1, visStart >> 8);
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175 outpw(CRTC_ADDR, 0x0D); /* set low byte */
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176 outpw(CRTC_ADDR+1, visStart & 0xff);
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180 * setXXXPage() sets the specified page by multiplying the page number
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181 * with the size of one page at the current resolution, then handing the
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182 * resulting offset value over to the corresponding setXXXStart()
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183 * function. The first page is number 0.
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186 void setActivePage(int page)
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188 setActiveStart(page * widthBytes * height);
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191 void setVisiblePage(int page)
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193 setVisibleStart(page * widthBytes * height);
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196 void putPixel_X(int x, int y, UCHAR color)
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199 /* Each address accesses four neighboring pixels, so set
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200 Write Plane Enable according to which pixel we want
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201 to modify. The plane is determined by the two least
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202 significant bits of the x-coordinate: */
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205 outp(0x3c5, 0x01 << (x & 3));
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207 /* The offset of the pixel into the video segment is
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208 offset = (width * y + x) / 4, and write the given
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209 color to the plane we selected above. Heed the active
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210 page start selection. */
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212 vga[(unsigned)(widthBytes * y) + (x / 4) + actStart] = color;
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216 UCHAR getPixel_X(int x, int y)
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219 /* Select the plane from which we must read the pixel color: */
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221 outpw(GRAC_ADDR, 0x04);
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222 outpw(GRAC_ADDR+1, x & 3);
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224 return vga[(unsigned)(widthBytes * y) + (x / 4) + actStart];
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228 void set320x240x256_X(void)
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231 /* Set the unchained version of mode 13h: */
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233 set320x200x256_X();
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235 /* Modify the vertical sync polarity bits in the Misc. Output
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236 Register to achieve square aspect ratio: */
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240 /* Modify the vertical timing registers to reflect the increased
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241 vertical resolution, and to center the image as good as
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244 outpw(0x3D4, 0x2C11); /* turn off write protect */
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245 outpw(0x3D4, 0x0D06); /* vertical total */
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246 outpw(0x3D4, 0x3E07); /* overflow register */
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247 outpw(0x3D4, 0xEA10); /* vertical retrace start */
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248 outpw(0x3D4, 0xAC11); /* vertical retrace end AND wr.prot */
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249 outpw(0x3D4, 0xDF12); /* vertical display enable end */
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250 outpw(0x3D4, 0xE715); /* start vertical blanking */
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251 outpw(0x3D4, 0x0616); /* end vertical blanking */
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253 /* Update mode info, so future operations are aware of the
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263 * The library testing routines follows below.
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272 void set80x25(void)
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276 int86(0x10, &r, &r);
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281 int p, x, y, pages;
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283 /* This is the way to calculate the number of pages available. */
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285 pages = 65536L/(widthBytes*height);
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287 for (p = 0; p < pages; ++p)
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291 /* On each page draw a single colored border, and dump the palette
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292 onto a small square about the middle of the page. */
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294 for (x = 0; x <= width; ++x)
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296 putPixel_X(x, 0, p+1);
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297 putPixel_X(x, height-1, p+1);
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300 for (y = 0; y <= height; ++y)
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302 putPixel_X(0, y, p+1);
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303 putPixel_X(width-1, y, p+1);
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306 for (x = 0; x < 16; ++x)
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307 for (y = 0; y < 16; ++y)
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308 putPixel_X(x+(p+3)*16, y+(p+3)*16, x + y*16);
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312 /* Each pages will now contain a different image. Let the user cycle
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313 through all the pages by pressing a key. */
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315 for (p = 0; p < pages; ++p)
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325 * Library test (program) entry point.
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330 // puts("First, have a look at the 320x200 mode. I will draw some rubbish");
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331 // puts("on all of the four pages, then let you cycle through them by");
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332 // puts("hitting a key on each page.");
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333 // puts("Press a key when ready...");
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336 // set320x200x256_X();
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340 // puts("Then, check out Mode X, 320x240 with 3 (and a half) pages.");
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341 // puts("Press a key when ready...");
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344 set320x240x256_X();
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348 puts("Where to next? It's your move!");
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