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A C64 game - Step 23

Posted by Endurion, in Uncategorized, C64 17 September 2011 · 607 views

Highscore display is all nice and dandy, but we want to see our score and name in there! So this step adds name entry. For this we rely on the Kernal (it's with 'a' on the C64) functions to read the pressed keys from the keyboard.

Adding to the score moving we find the spot for the name, shift all lower score names down and let the player enter his name.



Attached Image


The Kernal routine we're using is called GETIN and is placed in the ROM at $FFE4.



The following huge code snippet is placed in the old CheckForHighscore routine. For explanation reasons it's separated.



The first block moves the name entries of lower scores downwards. Remember, the name entries are stored continously in the location at HIGHSCORE_NAME.


          ;move names down
          ;shift older entries down, add new entry
          lda #( HIGHSCORE_ENTRY_COUNT - 1 )
          sta PARAM2
          
          ;y carries the offset in the score text, position at start of second last entry
          ldy #( ( HIGHSCORE_NAME_SIZE + 1 ) * ( HIGHSCORE_ENTRY_COUNT - 2 ) )
          
.CopyName
          lda PARAM2
          cmp PARAM1
          beq .SetNewName
          
          ;copy name
          ldx #0
          
.CopyNextNameChar
          lda HIGHSCORE_NAME,y
          sta HIGHSCORE_NAME + ( HIGHSCORE_NAME_SIZE + 1 ),y
          
          iny
          inx
          cpx #HIGHSCORE_NAME_SIZE
          bne .CopyNextNameChar
          
          tya
          sec
          sbc #( HIGHSCORE_NAME_SIZE + HIGHSCORE_NAME_SIZE + 1 )
          tay
          dec PARAM2
          jmp .CopyName



Here's the interesting part. First the proper offset of the new name inside the big text is calculated and the old name cleared out.

.SetNewName
          
          ;calc y for new name offset
          ldy PARAM1
          
          lda #0
.AddNameOffset          
          cpy #0
          beq .NameOffsetFound
          clc
          adc #( HIGHSCORE_NAME_SIZE + 1 )
          dey
          jmp .AddNameOffset
          
.NameOffsetFound          
          tay  

          ;clear old name
          ldx #0
          sty PARAM3
          lda #32
          
.ClearNextChar
          sta HIGHSCORE_NAME,y
          iny
          inx
          cpx #HIGHSCORE_NAME_SIZE
          bne .ClearNextChar


Here's the meat, the actual name entry. Of course with Backspace support and Enter to finalize the entry. Out of sheer lazyness the newly entered char is only inserted in the text and the text then fully displayed.

          ldy PARAM3
          
          ;enter name
          ldx #0
          stx PARAM3
          
          jmp .ShowChar
          
.GetNextChar
          sty PARAM4
          
          ;use ROM routines, read char
          jsr KERNAL_GETIN
          beq .GetNextChar

          ;return pressed?
          cmp #13
          beq .EnterPressed

          ;DEL pressed?
          cmp #20
          bne .NotDel
          
          ;DEL pressed
          ldy PARAM4
          ldx PARAM3
          beq .GetNextChar
          dec PARAM3
          dey
          dex
          lda #32
          sta HIGHSCORE_NAME,y
          jmp .ShowChar

.NotDel   
          ldy PARAM4
          ;pressed key >= 32 or <= 96?
          cmp #32
          bcc .GetNextChar
          cmp #96
          bcs .GetNextChar

          ;max length reached already?
          ldx PARAM3
          cpx #HIGHSCORE_NAME_SIZE
          bcs .GetNextChar
          
          ;save text
          sta HIGHSCORE_NAME,y
          iny
          inx
          
.ShowChar           
          stx PARAM3
          sty PARAM4

          ;display high scores
          ;x,y pos of name
          lda #6
          sta PARAM1
          lda #10
          sta PARAM2

          lda #<HIGHSCORE_NAME
          sta ZEROPAGE_POINTER_1
          lda #>HIGHSCORE_NAME
          sta ZEROPAGE_POINTER_1 + 1

          jsr DisplayText

          ldx PARAM3
          ldy PARAM4

          jmp .GetNextChar

.EnterPressed      
          ;fill entry with blanks
          lda #32
          ldx PARAM3
          ldy PARAM4
          
.FillNextChar          
          cpx #HIGHSCORE_NAME_SIZE
          beq .FilledUp
          sta HIGHSCORE_NAME,y
          iny
          inx
          jmp .FillNextChar          

.FilledUp
          jmp TitleScreen


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