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Add solution for Ex. 1
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README.md
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README.md
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#Apple ]\[ //e HGR Font 6502 Assembly Language Tutorial
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Revision: 35, Jan 14, 2016.
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Revision: 36, Jan 14, 2016.
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# Table of Contents
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@ -2143,6 +2143,149 @@ Michael "AppleWin Debug Dev"
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Figure it out ! You have all the tools and knowledge.
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Seriously though, start with the data flow. Let's look at the HGR "text" lines we need to copy from/to:
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Src Dst
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1 0
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2 1
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3 2
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4 3
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5 4
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6 5
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7 6
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8 7
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9 8
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10 9
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11 10
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12 11
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13 12
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14 13
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15 14
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16 15
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17 16
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18 17
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19 18
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20 19
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21 20
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22 21
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23 22
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-- 23
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We need to copy 23 HGR "text" lines to the one above; we also need to clear the bottom row. Pseudo-code would be:
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```C
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for( int line = 0; line < 24-1; line++
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copy_line( line+1, line );
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clear_line( 23 );
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```
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Each HGR "text" line takes up 40 columns
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```C
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for( int row = 0; row < 23; row++
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char *src = HGRAddressY[ row + 1 ]
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char *dst = HGRAddressY[ row + 0 ]
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for( int col = 0; col < 40; col++ )
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*dst++ = *src++;
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clear_line( 23 );
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```
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However each HGR "text" line takes 8 scanlines (since our font cell is 7x8).
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```C
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for( row = 0; row < 23; row++
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char *src = HGRAddressY[ row + 1 ]
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char *dst = HGRAddressY[ row + 0 ]
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for( line = 0; line < 8; line++ )
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{
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for( col = 0; col < 40; col++ )
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*dst++ = *src++;
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src += 0x400;
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dst += 0x400;
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}
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```
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We could code this up as:
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```assembly
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Src EQU $F8
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Dst EQU $FA
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Tmp EQU $FC
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; NOTE: Requires $E6 to be initialized with $20 or $40 for graphics page
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ORG $1900
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1900: ScrollHgrUpLine
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1900:A2 00 LDX #0 ; row
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; Copy Top 184 rows
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1902:BD A0 03 .1 LDA HgrLoY,X
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1905:85 FA STA Dst+0
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1907:BD B8 03 LDA HgrHiY,X
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190A:05 E6 ORA $E6
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190C:85 FB STA Dst+1
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190E:E8 INX
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190F:BD A0 03 LDA HgrLoY,X
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1912:85 F8 STA Src+0
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1914:BD B8 03 LDA HgrHiY,X
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1917:05 E6 ORA $E6
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1919:85 F9 STA Src+1
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191B:A9 07 LDA #7 ; 8 scanlines/text line
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191D:85 FC STA Tmp
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191F:A0 27 .2 LDY #40-1 ; 40 columns to copy
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1921:B1 F8 .3 LDA (Src),Y
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1923:91 FA STA (Dst),Y
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1925:88 DEY
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1926:10 F9 BPL .3 ; while (y-- > 0)
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1928:18 CLC
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1929:A5 F9 LDA Src+1
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192B:69 04 ADC #4
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192D:85 F9 STA Src+1
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192F:18 CLC
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1930:A5 FB LDA Dst+1
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1932:69 04 ADC #4
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1934:85 FB STA Dst+1
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1936:C6 FC DEC Tmp
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1938:10 E5 BPL .2
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193A:E0 17 CPX #23 ; 24 rows is #$18
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193C:90 C4 BCC .1 ; Y >= 23
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; Zero Bottom 8 scanlines ; $F8,$F9 = $D0,$43
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193E:A2 08 LDX #8 ; bottom 8 scanlines
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1940:38 CLC
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1941:A5 F9 LDA Src+1
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1943:E9 20 SBC #20
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1945:85 F9 STA Src+1
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1947:A9 00 .4 LDA #00 ; color = black
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1949:A0 27 LDY #40-1 ; 40 columns to copy
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194B:91 F8 .5 STA (Src),Y
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194D:88 DEY
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194E:10 FB BPL .5 ; while (y-- > 0)
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1950:18 CLC
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1951:A5 F9 LDA Src+1
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1953:69 04 ADC #4
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1955:85 F9 STA Src+1
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1957:CA DEX
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1958:D0 ED BNE .4 ; BNZ ; Try this fun bug: D0 EF
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195A:60 RTS
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```
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Enter in:
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1900:A2 00 BD A0 03 85 FA BD
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1908:B8 03 05 E6 85 FB E8 BD
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1910:A0 03 85 F8 BD B8 03 05
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1918:E6 85 F9 A9 07 85 FC A0
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1920:27 B1 F8 91 FA 88 10 F9
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1928:18 A5 F9 69 04 85 F9 18
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1930:A5 FB 69 04 85 FB C6 FC
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1938:10 E5 E0 17 90 C4 A2 08
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1940:38 A5 F9 E9 20 85 F9 A9
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1948:00 A0 27 91 F8 88 10 FB
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1950:18 A5 F9 69 04 85 F9 CA
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1958:D0 ED 60
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Excellent.
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## Solution 2: ScrollHgrUpPixel()
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There are many different ways to solve this depending if we want to prioritize space or speed.
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@ -2652,4 +2795,7 @@ That's all folks! Now go write some cool font blitter code.
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 (In progress)
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- [ ] Double Hi-Res
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- [ ] PDF of this document (As a work-around use Chrome and Print to PDF)
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- [ ] Explains `c/32` = `c / 2^5` = `c / (1 << 5)` = `c >> 5`
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- [ ] Fix mis-lable: We need to (again) touch up our `PrintChar` entry point at $0310 calling `_DrawChar2` ($034C)
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