Drawing pixels: yLookupLo

       Name: yLookupLo                                               [Show more]
       Type: Variable
   Category: Drawing pixels
    Summary: Lookup table for converting pixel y-coordinate to tile number
             (low byte)
    Context: See this variable in context in the source code
 References: This variable is used as follows:
             * DrawDash uses yLookupLo
             * DrawHangarWallLine uses yLookupLo
             * DrawSunRowOfBlocks uses yLookupLo
             * DrawVerticalLine (Part 1 of 3) uses yLookupLo
             * HAL3 uses yLookupLo
             * HAS3 uses yLookupLo
             * HLOIN (Part 1 of 5) uses yLookupLo
             * LOIN (Part 3 of 7) uses yLookupLo
             * LOIN (Part 4 of 7) uses yLookupLo
             * LOIN (Part 5 of 7) uses yLookupLo
             * PIXEL uses yLookupLo


 The NES screen mode is made up of 8x8-pixel tiles, with 32 tiles (256 pixels)
 across the screen, and either 30 tiles (240 pixels) or 28 tiles (224 pixels)
 vertically, for PAL or NTSC.

 This lookup table converts a pixel y-coordinate into the number of the first
 tile on the row containing the pixel. Pixel coordinate (0, 0) is mapped to the
 top-left pixel of the third row of tiles in the nametable, and the first
 column of tiles is at column 1 rather than 0 (as the screen is scrolled
 horizontally by 8 pixels via PPU_SCROLL), so pixel y-coordinates 0 to 7 are
 mapped to tile 65 (i.e. 2 * 32 + 1), pixel y-coordinates 8 to 15 are mapped to
 tile 97 (i.e. 3 * 32 + 1), and so on.


.yLookupLo

 FOR I%, 16, 239

  EQUB LO((I% DIV 8) * 32 + 1)

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