Isometric Source Code
by Geoff Howland

This is some old source code that I used to draw my isometric tiles, when I was doing it that way in the early stages of Force Recon. I was using the CDX library to handle DirectX then and there are a lot of global or outside variables that aren't documented in the routines very well simply because they were documented outside the code. I haven't cleaned this up since I first put it together and I'm not even sure the version of this code since I just grabbed it out of the middle of my old archive, I hope it helps in an algorithmic fashion though, which is how I'm intending it.

I reformatted this with tabs but I have not done anything else with it. The tabs will be lost in HTML format so download the text format to read them correctly.

Definitions:

mx,my = Map X/Y coordinates
sx,sy = Isometric screen coordinates
sax,say = Screen Actual coordinates, square tile version
xOffset,yOffset = Pixel offset from top left corner of current screen actual tile
mxOffset,myOffset = Offset of map tiles from the top left corner of the screen, for scrolling the map
ax,ay = Actual screen coordinates in pixels
sx,sy = Starting X/Y, usually for a comparison
ex,ey = Ending X/Y, usually for a comparison

void drawTiles(int wallVal)
{
  // Variables for drawing the map //
  int startX, startY=5; // Starting positions for drawing tiles // 
  // Y=5 seems to offset it correctly //
  int drawX=0, drawY=0; // Working positions for drawing tiles //
  int mapX=0-screen.mxOffset, mapY=-3-screen.myOffset; // For starting map positions //
  int tmapX=0, tmapY=0; // Temporary working map positions //
  int val=0; // Value for tile, for more than one tile and testing //
  // Draw Floor Map //
  for (int y=0; y < 52; y++) { //MAP_NUM_Y; y++) {
    if (y % 2 == 0) startX = 0; // Even Line //
    else   startX =  32; // Odd Line  //
    
    drawX = startX; drawY = startY; // Sync pix starts //
    tmapX = mapX; tmapY = mapY;  // Sync map starts //
    for (int x=0; x < 25; x++) { //MAP_NUM_X; x++) {
      val = checkMap(tmapX, tmapY);
      
      // Draw Floor //
      if (val == 1)
        tempSprites.AddSprite(FloorMap,0,drawX-TILE_X-64+screen.xOffset,drawY-TILE_X+screen.yOffset,0,0,0,1,0);
      
      else if (val == 0)
        tempSprites.AddSprite(FloorMap,0,drawX-TILE_X-64+screen.xOffset,drawY-TILE_X+screen.yOffset,0,0,0,0,0);
      
      // Draw walls where applicable //
      if (val == 3)
        tempSprites.AddSprite(Wall,0,drawX-WALL_X-64+screen.xOffset,drawY-WALL_Y+screen.yOffset,0,0,0,1,0);
      
      else if (val == 2)
        tempSprites.AddSprite(Wall,0,drawX-WALL_X-64+screen.xOffset,drawY-WALL_Y+screen.yOffset,0,0,0,0);
      
      else if (val == 4)
        tempSprites.AddSprite(Wall,0,drawX-WALL_X-64+screen.xOffset,drawY-WALL_Y+screen.yOffset,0,0,0,2,0);
      
      else if (val == 5)
        tempSprites.AddSprite(Wall,0,drawX-WALL_X-64+screen.xOffset,drawY-WALL_Y+screen.yOffset,0,0,0,3,0);
      
      // Increment X for the next tile //
      drawX += TILE_X;
      
      // Increment Map values //
      tmapX+=1;
      tmapY+=1;
    }
    
    // Increment Y for next line //
    startY += 15; // Y for new ground (64x30)
    
    // Adjust starting position of map for next line //
    if (y%2 == 0) { // Even //
      mapY+=1;
    }
    else { // Odd //
      mapX-=1;
    }
  }
  ///// End walls draw /////
}

void scrollScreen(int x, int y)
{
  // Increment Screen pixel offsets //
  screen.xOffset += x;
  screen.yOffset += y;
  
  // Increment Map tile offset //
  // x offset //
  if (screen.xOffset > 63) {
    screen.mxOffset += 1;
    screen.myOffset += 1;
    screen.xOffset = screen.xOffset - 64;
  }
  else if (screen.xOffset < 0) {
    screen.mxOffset += -1;
    screen.myOffset += -1;
    screen.xOffset = screen.xOffset + 64;
  }
  // y offset //
  if (screen.yOffset > 29) {
    screen.mxOffset += -1;
    screen.myOffset += 1;
    screen.yOffset = screen.yOffset - 30;
  }
  else if (screen.yOffset < 0) {
    screen.mxOffset += 1;
    screen.myOffset += -1;
    screen.yOffset = screen.yOffset + 30;
  }
  // End Incrementing Map tile offset //
}

// Checks tile value on coordinate of map //
int checkMap(int x, int y)
{
  int val=0;
  
  if (x < 0 || y < 0)
    return (-1);
  
  val = Map1[x+(MAP_NUM_X*y)];
  
  return (val);
}

Mouse Routines

void mouseConvert()
{
  // Modify tmx,tmy with the tileX,tileY //
  mouse.tmx += TILE_X; mouse.tmy += TILE_Y;
  
  // Get Tile X,Y //
  mouse.tx = mouse.tmx / 64;
  mouse.ty = mouse.tmy / 30;
  // Get Mouse X,Y //
  mouse.mx = mouse.tmx % 64;
  mouse.my = mouse.tmy % 30;
  
  // Determine what tile from center tile //
  if (mouse.my < 14) { // Mouse is on top part //
    mouse.sx = 29 + (-2 * mouse.my); // Interpolate edges //
    mouse.ex = 33 + (2 * mouse.my);
    if (mouse.mx < mouse.sx) {
      mouse.ax = -1; mouse.ay = -1;
    }
    else if (mouse.mx > mouse.ex) {
      mouse.ax = 1; mouse.ay = -1;
    }
    else {
      mouse.ax = 0; mouse.ay = 0;
    }
  }
  else if (mouse.my > 14) { // Mouse is on bottom part //
    mouse.sx = 29 + (-2 * (29 - mouse.my)); // Interpolate edges //
    mouse.ex = 33 + (2 * (29 - mouse.my));
    if (mouse.mx < mouse.sx) {
      mouse.ax = -1; mouse.ay = 1;
    }
    else if (mouse.mx > mouse.ex) {
      mouse.ax = 1; mouse.ay = 1;
    }
    else {
      mouse.ax = 0; mouse.ay = 0;
    }
  }
  else { // Middle line is automatic //
    mouse.ax = 0; mouse.ay = 0;
  }
  
  // Decode ax and ay to figure out the screen tiles //
  if (mouse.ay < 0) { // Above center tile //
    if (mouse.ax < 0) { // Left of center tile //
      mouse.sax = mouse.tx; mouse.say = (mouse.ty * 2) -1;
    }
    if (mouse.ax > 0) { // Right of center tile //
      mouse.sax = mouse.tx+1; mouse.say = (mouse.ty * 2) -1;
    }
  }
	else if (mouse.ay > 0) { // Below center tile //
		if (mouse.ax < 0) { // Left of center tile //
			mouse.sax = mouse.tx; mouse.say = (mouse.ty * 2) +1;
		}
		if (mouse.ax > 0) { // Right of center tile //
			mouse.sax = mouse.tx+1; mouse.say = (mouse.ty * 2) +1;
		}
  }
  else {
    mouse.sax = mouse.tx; mouse.say = mouse.ty *2;
  }
  // End ax and ay Decode //
  
  // Decrement Screen Actual X and Y //
  mouse.mx = mouse.sax-1; // Init the map coords //
  mouse.my = mouse.say-1;
  
  // Convert Screen to Map Coords //
  mouse.mx = mouse.mx - (mouse.my / 2); // Dividing by two gives the number of X's to move over for 0x for my lines down //
  mouse.my = mouse.my + mouse.mx; // Adding mx to my will also offset the upwards slope that each Y line has //
  
  /* if (mouse.mx < 0) // If mx is negative then cross the map //
  mouse.mx = MAP_NUM_X + mouse.mx;*/
}

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Date this article was posted to GameDev.net: 9/14/1999
(Note that this date does not necessarily correspond to the date the article was written)

See Also:
General