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  1. /*********************************************************************
  2. This is a library for our Monochrome OLEDs based on SSD1306 drivers
  3.  
  4.   Pick one up today in the adafruit shop!
  5.   ------> http://www.adafruit.com/category/63_98
  6.  
  7. These displays use SPI to communicate, 4 or 5 pins are required to  
  8. interface
  9.  
  10. Adafruit invests time and resources providing this open source code,
  11. please support Adafruit and open-source hardware by purchasing
  12. products from Adafruit!
  13.  
  14. Written by Limor Fried/Ladyada  for Adafruit Industries.  
  15. BSD license, check license.txt for more information
  16. All text above, and the splash screen below must be included in any redistribution
  17.  
  18. This code is taken from the ADAfruit library - it is used for playing with an OLED screen
  19.  
  20. *********************************************************************/
  21. #include <stdint.h>
  22. #include <string.h>
  23. #include "stm32f1xx_hal.h"
  24. #include "SSD1306.h"
  25.  
  26.  
  27. #define swap(x,y) { typeof(x)t = x; x=y; y=t; }
  28. #define abs(x)      ((x)>0?(x):-(x))
  29.  
  30. static uint8_t rotation = 0;
  31. const uint16_t WIDTH  = SSD1306_LCDWIDTH;
  32. const uint16_t HEIGHT = SSD1306_LCDHEIGHT;
  33.  
  34. extern SPI_HandleTypeDef hspi1;
  35.  
  36.  
  37.  
  38.  
  39. // the memory buffer for the LCD
  40.  
  41. // pointer to the current display - affects buffer used and also chipselect
  42. static int cd = 0;
  43.  
  44. uint8_t display_buffer[MAX_PHYS_DISPLAYS][SSD1306_LCDHEIGHT * SSD1306_LCDWIDTH / 8];
  45.  
  46. inline uint8_t * display_address(void)
  47. {
  48.         return (uint8_t *)(&display_buffer[cd]);
  49. }
  50.  
  51. inline uint8_t getRotation(void)
  52. {
  53.         return rotation;
  54. }
  55.  
  56. inline int16_t width(void)
  57. {
  58.         switch (rotation)
  59.         {
  60.         case 0:
  61.                 return WIDTH;
  62.                 break;
  63.         case 1:
  64.                 return WIDTH;
  65.                 break;
  66.         case 2:
  67.                 return HEIGHT;
  68.                 break;
  69.         case 3:
  70.                 return -WIDTH;
  71.                 break;
  72.     }
  73.   return 0;
  74. }
  75.  
  76. inline int16_t height(void)
  77. {
  78.         switch (rotation)
  79.         {
  80.         case 0:
  81.                 return HEIGHT;
  82.                 break;
  83.         case 1:
  84.                 return HEIGHT;
  85.                 break;
  86.         case 2:
  87.                 return WIDTH;
  88.                 break;
  89.         case 3:
  90.                 return -HEIGHT;
  91.                 break;
  92.     }
  93.         return 0;
  94. }
  95.  
  96.  
  97. inline void fastSPIwrite(uint8_t d)
  98. {
  99.   uint8_t buffer[1];
  100.   buffer[0] = d;
  101. // todo chipselect based on 'cd' buffer choice
  102.  
  103.   HAL_SPI_Transmit(&hspi1, buffer, 1, 2);
  104.  
  105. }
  106.  
  107.  
  108. // the most basic function, set a single pixel
  109. inline void drawPixel(int16_t x, int16_t y, uint16_t color) {
  110.   if ((x < 0) || (x >= width()) || (y < 0) || (y >= height()))
  111.     return;
  112.  
  113.   // check rotation, move pixel around if necessary
  114.   switch (getRotation()) {
  115.   case 1:
  116.     swap(x, y);
  117.     x = WIDTH - x - 1;
  118.     break;
  119.   case 2:
  120.     x = WIDTH - x - 1;
  121.     y = HEIGHT - y - 1;
  122.     break;
  123.   case 3:
  124.     swap(x, y);
  125.     y = HEIGHT - y - 1;
  126.     break;
  127.   }  
  128.  
  129.   // x is which column
  130.   switch(color)
  131.   {
  132.   case BLACK:
  133.     display_buffer[cd][x+ (y/8)*SSD1306_LCDWIDTH] &= ~(1 << (y&7));
  134.     break;
  135.  
  136.   default:
  137.   case  WHITE:
  138.     display_buffer[cd][x+ (y/8)*SSD1306_LCDWIDTH] |= (1 << (y&7));
  139.     break;
  140.  
  141.   case  INVERT:
  142.         display_buffer[cd][x+ (y/8)*SSD1306_LCDWIDTH] ^= (1 << (y&7));
  143.         break;
  144.   }
  145. }
  146.  
  147.  
  148.  
  149.  
  150. void ssd1306_begin(uint8_t vccstate, uint8_t i2caddr) {
  151.  
  152.  
  153.    HAL_GPIO_WritePin(SPI_RESET_GPIO_Port,SPI_RESET_Pin,GPIO_PIN_SET);
  154.  
  155.   // VDD (3.3V) goes high at start, lets just chill for a ms
  156.   HAL_Delay(1);
  157.   // bring reset low
  158.   HAL_GPIO_WritePin(SPI_RESET_GPIO_Port,SPI_RESET_Pin,GPIO_PIN_RESET);
  159.   // wait 10ms
  160.   HAL_Delay(10);
  161.   // bring out of reset
  162.   HAL_GPIO_WritePin(SPI_RESET_GPIO_Port,SPI_RESET_Pin,GPIO_PIN_SET);
  163.   // turn on VCC (9V?)
  164.  
  165.   for(cd = 0; cd<2 ; cd++)
  166.   {
  167.    #if defined SSD1306_128_32
  168.     // Init sequence for 128x32 OLED module
  169.     ssd1306_command(SSD1306_DISPLAYOFF);                    // 0xAE
  170.     ssd1306_command(SSD1306_SETDISPLAYCLOCKDIV);            // 0xD5
  171.     ssd1306_command(0x80);                                  // the suggested ratio 0x80
  172.     ssd1306_command(SSD1306_SETMULTIPLEX);                  // 0xA8
  173.     ssd1306_command(0x1F);
  174.     ssd1306_command(SSD1306_SETDISPLAYOFFSET);              // 0xD3
  175.     ssd1306_command(0x0);                                   // no offset
  176.     ssd1306_command(SSD1306_SETSTARTLINE | 0x0);            // line #0
  177.     ssd1306_command(SSD1306_CHARGEPUMP);                    // 0x8D
  178.     if (vccstate == SSD1306_EXTERNALVCC)
  179.       { ssd1306_command(0x10); }
  180.     else
  181.       { ssd1306_command(0x14); }
  182.     ssd1306_command(SSD1306_MEMORYMODE);                    // 0x20
  183.     ssd1306_command(0x00);                                  // 0x0 act like ks0108
  184.         ssd1306_command(SSD1306_SEGREMAP | 0x1);
  185.     ssd1306_command(SSD1306_COMSCANDEC);
  186.     ssd1306_command(SSD1306_SETCOMPINS);                    // 0xDA
  187.     ssd1306_command(0x02);
  188.     ssd1306_command(SSD1306_SETCONTRAST);                   // 0x81
  189.     ssd1306_command(0x8F);
  190.     ssd1306_command(SSD1306_SETPRECHARGE);                  // 0xd9
  191.     if (vccstate == SSD1306_EXTERNALVCC)
  192.       { ssd1306_command(0x22); }
  193.     else
  194.       { ssd1306_command(0xF1); }
  195.     ssd1306_command(SSD1306_SETVCOMDETECT);                 // 0xDB
  196.     ssd1306_command(0x40);
  197.     ssd1306_command(SSD1306_DISPLAYALLON_RESUME);           // 0xA4
  198.     ssd1306_command(SSD1306_NORMALDISPLAY);                 // 0xA6
  199.   #endif
  200.  
  201.   #if defined SSD1306_128_64
  202.     // Init sequence for 128x64 OLED module
  203.     ssd1306_command(SSD1306_DISPLAYOFF);                    // 0xAE
  204.     ssd1306_command(SSD1306_SETDISPLAYCLOCKDIV);            // 0xD5
  205.     ssd1306_command(0x80);                                  // the suggested ratio 0x80
  206.     ssd1306_command(SSD1306_SETMULTIPLEX);                  // 0xA8
  207.     ssd1306_command(0x3F);
  208.     ssd1306_command(SSD1306_SETDISPLAYOFFSET);              // 0xD3
  209.     ssd1306_command(0x0);                                   // no offset
  210.     ssd1306_command(SSD1306_SETSTARTLINE | 0x0);            // line #0
  211.     ssd1306_command(SSD1306_CHARGEPUMP);                    // 0x8D
  212.     if (vccstate == SSD1306_EXTERNALVCC)
  213.       { ssd1306_command(0x10); }
  214.     else
  215.       { ssd1306_command(0x14); }
  216.     ssd1306_command(SSD1306_MEMORYMODE);                    // 0x20
  217.     ssd1306_command(0x00);                                  // 0x0 act like ks0108
  218.     ssd1306_command(SSD1306_SEGREMAP | 0x1);
  219.     ssd1306_command(SSD1306_COMSCANDEC);
  220.     ssd1306_command(SSD1306_SETCOMPINS);                    // 0xDA
  221.     ssd1306_command(0x12);
  222.     ssd1306_command(SSD1306_SETCONTRAST);                   // 0x81
  223.     if (vccstate == SSD1306_EXTERNALVCC)
  224.       { ssd1306_command(0x9F); }
  225.     else
  226.       { ssd1306_command(0xCF); }
  227.     ssd1306_command(SSD1306_SETPRECHARGE);                  // 0xd9
  228.     if (vccstate == SSD1306_EXTERNALVCC)
  229.       { ssd1306_command(0x22); }
  230.     else
  231.       { ssd1306_command(0xF1); }
  232.     ssd1306_command(SSD1306_SETVCOMDETECT);                 // 0xDB
  233.     ssd1306_command(0x40);
  234.     ssd1306_command(SSD1306_DISPLAYALLON_RESUME);           // 0xA4
  235.     ssd1306_command(SSD1306_NORMALDISPLAY);                 // 0xA6
  236.   #endif
  237.  
  238.   ssd1306_command(SSD1306_DISPLAYON);//--turn on oled panel
  239.   }
  240. }
  241.  
  242.  
  243. void invertDisplay(uint8_t i) {
  244.   if (i) {
  245.     ssd1306_command(SSD1306_INVERTDISPLAY);
  246.   } else {
  247.     ssd1306_command(SSD1306_NORMALDISPLAY);
  248.   }
  249. }
  250.  
  251. void ssd1306_command(uint8_t c)
  252. {
  253.         HAL_GPIO_WritePin(SPI1CD_GPIO_Port,SPI1CD_Pin,GPIO_PIN_RESET);
  254.  
  255.     fastSPIwrite(c);
  256.  
  257. }
  258.  
  259. // startscrollright
  260. // Activate a right handed scroll for rows start through stop
  261. // Hint, the display is 16 rows tall. To scroll the whole display, run:
  262. // display.scrollright(0x00, 0x0F)
  263. void startscrollright(uint8_t start, uint8_t stop){
  264.         ssd1306_command(SSD1306_RIGHT_HORIZONTAL_SCROLL);
  265.         ssd1306_command(0X00);
  266.         ssd1306_command(start);
  267.         ssd1306_command(0X00);
  268.         ssd1306_command(stop);
  269.         ssd1306_command(0X00);
  270.         ssd1306_command(0XFF);
  271.         ssd1306_command(SSD1306_ACTIVATE_SCROLL);
  272. }
  273.  
  274. // startscrollleft
  275. // Activate a right handed scroll for rows start through stop
  276. // Hint, the display is 16 rows tall. To scroll the whole display, run:
  277. // display.scrollright(0x00, 0x0F)
  278. void startscrollleft(uint8_t start, uint8_t stop){
  279.         ssd1306_command(SSD1306_LEFT_HORIZONTAL_SCROLL);
  280.         ssd1306_command(0X00);
  281.         ssd1306_command(start);
  282.         ssd1306_command(0X00);
  283.         ssd1306_command(stop);
  284.         ssd1306_command(0X00);
  285.         ssd1306_command(0XFF);
  286.         ssd1306_command(SSD1306_ACTIVATE_SCROLL);
  287. }
  288.  
  289. // startscrolldiagright
  290. // Activate a diagonal scroll for rows start through stop
  291. // Hint, the display is 16 rows tall. To scroll the whole display, run:
  292. // display.scrollright(0x00, 0x0F)
  293. void startscrolldiagright(uint8_t start, uint8_t stop){
  294.         ssd1306_command(SSD1306_SET_VERTICAL_SCROLL_AREA);     
  295.         ssd1306_command(0X00);
  296.         ssd1306_command(SSD1306_LCDHEIGHT);
  297.         ssd1306_command(SSD1306_VERTICAL_AND_RIGHT_HORIZONTAL_SCROLL);
  298.         ssd1306_command(0X00);
  299.         ssd1306_command(start);
  300.         ssd1306_command(0X00);
  301.         ssd1306_command(stop);
  302.         ssd1306_command(0X01);
  303.         ssd1306_command(SSD1306_ACTIVATE_SCROLL);
  304. }
  305.  
  306. // startscrolldiagleft
  307. // Activate a diagonal scroll for rows start through stop
  308. // Hint, the display is 16 rows tall. To scroll the whole display, run:
  309. // display.scrollright(0x00, 0x0F)
  310. void startscrolldiagleft(uint8_t start, uint8_t stop){
  311.         ssd1306_command(SSD1306_SET_VERTICAL_SCROLL_AREA);     
  312.         ssd1306_command(0X00);
  313.         ssd1306_command(SSD1306_LCDHEIGHT);
  314.         ssd1306_command(SSD1306_VERTICAL_AND_LEFT_HORIZONTAL_SCROLL);
  315.         ssd1306_command(0X00);
  316.         ssd1306_command(start);
  317.         ssd1306_command(0X00);
  318.         ssd1306_command(stop);
  319.         ssd1306_command(0X01);
  320.         ssd1306_command(SSD1306_ACTIVATE_SCROLL);
  321. }
  322.  
  323. void stopscroll(void){
  324.         ssd1306_command(SSD1306_DEACTIVATE_SCROLL);
  325. }
  326.  
  327. // Dim the display
  328. // dim = true: display is dimmed
  329. // dim = false: display is normal
  330. void dim(boolean dim) {
  331.   uint8_t contrast;
  332.  
  333.   if (dim) {
  334.     contrast = 0; // Dimmed display
  335.   } else {
  336.       contrast = 0xCF;
  337.   }
  338.   // the range of contrast to too small to be really useful
  339.   // it is useful to dim the display
  340.   ssd1306_command(SSD1306_SETCONTRAST);
  341.   ssd1306_command(contrast);
  342. }
  343.  
  344. void display(void) {
  345.   ssd1306_command(SSD1306_COLUMNADDR);
  346.   ssd1306_command(0);   // Column start address (0 = reset)
  347.   ssd1306_command(131); // Column end address (127 = reset)
  348.  
  349.   ssd1306_command(SSD1306_PAGEADDR);
  350.   ssd1306_command(0); // Page start address (0 = reset)
  351.   ssd1306_command((SSD1306_LCDHEIGHT == 64) ? 7 : 3); // Page end address
  352.  
  353.   int row;
  354.   int col=2;
  355.   for(row=0;row<SSD1306_LCDHEIGHT/8;row++)
  356.   {
  357.      // set the cursor to
  358.           ssd1306_command(0xB0 + row);//set page address
  359.           ssd1306_command(col & 0xf);//set lower column address
  360.           ssd1306_command(0x10 | (col >> 4));//set higher column address
  361.  
  362.  
  363.       HAL_GPIO_WritePin(SPI1CD_GPIO_Port,SPI1CD_Pin,GPIO_PIN_SET);
  364.       HAL_SPI_Transmit(&hspi1, (uint8_t *)(&display_buffer[cd])+row*SSD1306_LCDWIDTH, SSD1306_LCDWIDTH, 100);
  365.       }
  366.  
  367. }
  368.  
  369.  
  370. // clear everything
  371. void clearDisplay(void) {
  372.   memset(&display_buffer[cd], 0, (SSD1306_LCDWIDTH*SSD1306_LCDHEIGHT/8));
  373. }
  374.  
  375.  
  376. void drawFastHLine(int16_t x, int16_t y, int16_t w, uint16_t color) {
  377.   boolean bSwap = false;
  378.   switch(rotation) {
  379.     case 0:
  380.       // 0 degree rotation, do nothing
  381.       break;
  382.     case 1:
  383.       // 90 degree rotation, swap x & y for rotation, then invert x
  384.       bSwap = true;
  385.       swap(x, y);
  386.       x = WIDTH - x - 1;
  387.       break;
  388.     case 2:
  389.       // 180 degree rotation, invert x and y - then shift y around for height.
  390.       x = WIDTH - x - 1;
  391.       y = HEIGHT - y - 1;
  392.       x -= (w-1);
  393.       break;
  394.     case 3:
  395.       // 270 degree rotation, swap x & y for rotation, then invert y  and adjust y for w (not to become h)
  396.       bSwap = true;
  397.       swap(x, y);
  398.       y = HEIGHT - y - 1;
  399.       y -= (w-1);
  400.       break;
  401.   }
  402.  
  403.   if(bSwap) {
  404.     drawFastVLineInternal(x, y, w, color);
  405.   } else {
  406.     drawFastHLineInternal(x, y, w, color);
  407.   }
  408. }
  409.  
  410. void drawFastHLineInternal(int16_t x, int16_t y, int16_t w, uint16_t color) {
  411.   // Do bounds/limit checks
  412.   if(y < 0 || y >= HEIGHT) { return; }
  413.  
  414.   // make sure we don't try to draw below 0
  415.   if(x < 0) {
  416.     w += x;
  417.     x = 0;
  418.   }
  419.  
  420.   // make sure we don't go off the edge of the display
  421.   if( (x + w) > WIDTH) {
  422.     w = (HEIGHT- x);
  423.   }
  424.  
  425.   // if our width is now negative, punt
  426.   if(w <= 0) { return; }
  427.  
  428.   // set up the pointer for  movement through the buffer
  429.   register uint8_t *pBuf = display_address();
  430.   // adjust the buffer pointer for the current row
  431.   pBuf += ((y/8) * SSD1306_LCDWIDTH);
  432.   // and offset x columns in
  433.   pBuf += x;
  434.  
  435.   register uint8_t mask = 1 << (y&7);
  436.  
  437.   if(color == WHITE) {
  438.     while(w--) { *pBuf++ |= mask; }
  439.   } else {
  440.     mask = ~mask;
  441.     while(w--) { *pBuf++ &= mask; }
  442.   }
  443. }
  444.  
  445. void drawFastVLine(int16_t x, int16_t y, int16_t h, uint16_t color) {
  446.   boolean bSwap = false;
  447.   switch(rotation) {
  448.     case 0:
  449.       break;
  450.     case 1:
  451.       // 90 degree rotation, swap x & y for rotation, then invert x and adjust x for h (now to become w)
  452.       bSwap = true;
  453.       swap(x, y);
  454.       x = WIDTH - x - 1;
  455.       x -= (h-1);
  456.       break;
  457.     case 2:
  458.       // 180 degree rotation, invert x and y - then shift y around for height.
  459.       x = WIDTH - x - 1;
  460.       y = HEIGHT - y - 1;
  461.       y -= (h-1);
  462.       break;
  463.     case 3:
  464.       // 270 degree rotation, swap x & y for rotation, then invert y
  465.       bSwap = true;
  466.       swap(x, y);
  467.       y = HEIGHT - y - 1;
  468.       break;
  469.   }
  470.  
  471.   if(bSwap) {
  472.     drawFastHLineInternal(x, y, h, color);
  473.   } else {
  474.     drawFastVLineInternal(x, y, h, color);
  475.   }
  476. }
  477.  
  478.  
  479. void drawFastVLineInternal(int16_t x, int16_t __y, int16_t __h, uint16_t color) {
  480.  
  481.   // do nothing if we're off the left or right side of the screen
  482.   if(x < 0 || x >= WIDTH) { return; }
  483.  
  484.   // make sure we don't try to draw below 0
  485.   if(__y < 0) {
  486.     // __y is negative, this will subtract enough from __h to account for __y being 0
  487.     __h += __y;
  488.     __y = 0;
  489.  
  490.   }
  491.  
  492.   // make sure we don't go past the height of the display
  493.   if( (__y + __h) > HEIGHT) {
  494.     __h = (HEIGHT - __y);
  495.   }
  496.  
  497.   // if our height is now negative, punt
  498.   if(__h <= 0) {
  499.     return;
  500.   }
  501.  
  502.   // this display doesn't need ints for coordinates, use local byte registers for faster juggling
  503.   register uint8_t y = __y;
  504.   register uint8_t h = __h;
  505.  
  506.  
  507.   // set up the pointer for fast movement through the buffer
  508.   register uint8_t *pBuf = display_address();
  509.   // adjust the buffer pointer for the current row
  510.   pBuf += ((y/8) * SSD1306_LCDWIDTH);
  511.   // and offset x columns in
  512.   pBuf += x;
  513.  
  514.   // do the first partial byte, if necessary - this requires some masking
  515.   register uint8_t mod = (y&7);
  516.   if(mod) {
  517.     // mask off the high n bits we want to set
  518.     mod = 8-mod;
  519.  
  520.     // note - lookup table results in a nearly 10% performance improvement in fill* functions
  521.     // register uint8_t mask = ~(0xFF >> (mod));
  522.     static uint8_t premask[8] = {0x00, 0x80, 0xC0, 0xE0, 0xF0, 0xF8, 0xFC, 0xFE };
  523.     register uint8_t mask = premask[mod];
  524.  
  525.     // adjust the mask if we're not going to reach the end of this byte
  526.     if( h < mod) {
  527.       mask &= (0XFF >> (mod-h));
  528.     }
  529.  
  530.     if(color == WHITE) {
  531.       *pBuf |= mask;
  532.     } else {
  533.       *pBuf &= ~mask;
  534.     }
  535.  
  536.     // fast exit if we're done here!
  537.     if(h<mod) { return; }
  538.  
  539.     h -= mod;
  540.  
  541.     pBuf += SSD1306_LCDWIDTH;
  542.   }
  543.  
  544.  
  545.   // write solid bytes while we can - effectively doing 8 rows at a time
  546.   if(h >= 8) {
  547.     // store a local value to work with
  548.     register uint8_t val = (color == WHITE) ? 255 : 0;
  549.  
  550.     do  {
  551.       // write our value in
  552.       *pBuf = val;
  553.  
  554.       // adjust the buffer forward 8 rows worth of data
  555.       pBuf += SSD1306_LCDWIDTH;
  556.  
  557.       // adjust h & y (there's got to be a faster way for me to do this, but this should still help a fair bit for now)
  558.       h -= 8;
  559.     } while(h >= 8);
  560.   }
  561.  
  562.   // now do the final partial byte, if necessary
  563.   if(h) {
  564.     mod = h & 7;
  565.     // this time we want to mask the low bits of the byte, vs the high bits we did above
  566.     // register uint8_t mask = (1 << mod) - 1;
  567.     // note - lookup table results in a nearly 10% performance improvement in fill* functions
  568.     static uint8_t postmask[8] = {0x00, 0x01, 0x03, 0x07, 0x0F, 0x1F, 0x3F, 0x7F };
  569.     register uint8_t mask = postmask[mod];
  570.     if(color == WHITE) {
  571.       *pBuf |= mask;
  572.     } else {
  573.       *pBuf &= ~mask;
  574.     }
  575.   }
  576. }
  577.  
  578.  
  579.  
  580.  
  581. /* using Bresenham draw algorithm */
  582. void drawLine(int16_t x1, int16_t y1, int16_t x2, int16_t y2, uint8_t color)
  583. {
  584.         int16_t x,
  585.                         y,
  586.                         dx,             //deltas
  587.             dy,
  588.             dx2,        //scaled deltas
  589.             dy2,
  590.             ix,         //increase rate on the x axis
  591.             iy,         //increase rate on the y axis
  592.             err;        //the error term
  593.     uint16_t i;         //looping variable
  594.  
  595.  
  596.         // identify the first pixel
  597.         x=x1;
  598.         y=y1;
  599.  
  600.         // difference between starting and ending points
  601.         dx = x2 - x1;
  602.         dy = y2 - y1;
  603.  
  604.         // calculate direction of the vector and store in ix and iy
  605.         if (dx >= 0)
  606.                 ix = 1;
  607.  
  608.         if (dx < 0)
  609.         {
  610.                 ix = -1;
  611.                 dx = abs(dx);
  612.         }
  613.  
  614.         if (dy >= 0)
  615.                 iy = 1;
  616.  
  617.         if (dy < 0)
  618.         {
  619.                 iy = -1;
  620.                 dy = abs(dy);
  621.         }
  622.  
  623.         // scale deltas and store in dx2 and dy2
  624.         dx2 = dx * 2;
  625.         dy2 = dy * 2;
  626.  
  627. // all  variables are set and it's time to enter the main loop.
  628.  
  629.         if (dx > dy)    // dx is the major axis
  630.         {
  631.                 // initialize the error term
  632.                 err = dy2 - dx;
  633.  
  634.                 for (i = 0; i <= dx; i++)
  635.                 {
  636.                         drawPixel(x, y, color);
  637.                         if (err >= 0)
  638.                         {
  639.                                 err -= dx2;
  640.                                 y += iy;
  641.                         }
  642.                         err += dy2;
  643.                         x += ix;
  644.                 }
  645.         }
  646.  
  647.         else            // dy is the major axis
  648.         {
  649.                 // initialize the error term
  650.                 err = dx2 - dy;
  651.  
  652.                 for (i = 0; i <= dy; i++)
  653.                 {
  654.                         drawPixel(x, y, color);
  655.                         if (err >= 0)
  656.                         {
  657.                                 err -= dy2;
  658.                                 x += ix;
  659.                         }
  660.                         err += dx2;
  661.                         y += iy;
  662.                 }
  663.         }
  664. }
  665.  
  666.  
  667. void select_display(int i)
  668. {
  669.         if(i<MAX_PHYS_DISPLAYS)
  670.         {
  671.                 cd = i;
  672.         }
  673. }
  674.