an additional label in <library-asm/print.asm>

[programandala.net]

This can be done by modifying the print routine. ZX Basic does not use the ROM print routine but its own (faster and more featured) one. If you need a print system that does not use UDG but all chars this can be achieved by patching the print.asm library with an #ifdef directive (you can specify special Defines from the command line with zxb -D TAG).

Of course. I did it four years ago. But the problem is the changes in <print.asm> are lost when ZX BASIC is updated. What I have written now is a simple library that switches on and off the new print mode, while the program is running. See the code of my proposed library:

Code:

' charset224.zxbas ' Version A-00-20140511 ' An addon for ZX BASIC (http://zxbasic.net) ' Copyright (C) 2014 Marcos Cruz (programandala.net) ' This file is released under the GPL v3 License ' -------------------------------------------------------------- ' Description ' This ZX BASIC file provides a sub called 'charset224'. It activates ' or deactivates a new printing mode. In the new mode, all 224 chars ' from 0x20 to 0xFF are printed as ordinary chars from the standard ' charset pointed by the CHARS system variable (no UDG, no block ' graphics, no tokens). Of course in order to use the new mode a ' proper 224-char font has to be in memory and CHARS has to be changed ' accordingly. ' The objective is to use a standard 8-bit character set (e.g. Latin ' 1) in ZX BASIC programs. This is very useful for programs in other ' languages than English, especially for programs that need a lot of ' text (text adventures or certain applications): No special notation ' or tricks are required in order to use standard non-ASCII chars into ' the texts the program will show at run-time. ' A 224-char font ocuppies 1792 bytes, and probably most of the chars ' will not be required by most programs, but the space of the unused ' chars can be used for graphics, data or even Z80 code. ' -------------------------------------------------------------- ' Idea for an improved version ' A new printing mode to use the new font only for chars greater than ' 0x7E. This option would save 752 bytes. This mode would be useful ' for large programs that do not need a whole 255-bit new font design, ' but just need to add the missing standard non-ASCII chars to the ' ordinary ZX Spectrum font. ' -------------------------------------------------------------- ' Change log ' 2014-05-06: First simple version. The parameter of the sub is the ' jump opcode required to hack the original <library-asm/print.asm> ' with. Two lines of code have to be previously and permanently ' modified in <library-asm/print.asm>. ' 2014-05-11: The code was rewritten and improved with a different ' approach: The original <library-asm/print.asm> has not to be ' previously modified, only a new label has to be added to it. All ' required changes are done by the sub. Its parameter is just a flag. ' The program is renamed. ' -------------------------------------------------------------- #ifndef __LIBRARY_CHARSET224__ ' Avoid recursive / multiple inclusion #define __LIBRARY_CHARSET224__ sub fastcall charset224(flag as ubyte) ' This sub modifies the Z80 code of ZX BASIC's ' <library-asm/print.asm>, in order to change its behaviour. ' If flag=0 ' the legacy ZX Spectrum charset printing mode is set ' (ordinary chars, UDG and block graphics are managed differently). ' This is the original behaviour of the printing routine. ' If flag<>0 ' the modern 8-bit charset printing mode is set ' (all chars 20h-FFh are ordinary). asm proc ld hl,JUMP_IF_GREATER_THAN_80H ; address of the jump to be modified and a jr nz,MODIFY_THE_ORIGINAL_CODE local RESTORE_THE_ORIGINAL_CODE RESTORE_THE_ORIGINAL_CODE: ; Set the legacy ZX Spectrum charset printing mode ld (HL),218 ; = 0xDA = Z80's 'JP C' call READY ; original code add a, a ; 1 byte ld l, a ; 1 byte ld h, 0 ; 2 bytes local MODIFY_THE_ORIGINAL_CODE MODIFY_THE_ORIGINAL_CODE: ; Set the modern 8-bit charset printing mode ld (HL),195 ; = 0xC3 = Z80's 'JP' call READY ; code to overwrite the original version with ld l, a ; 1 byte ld h, 0 ; 2 bytes add hl,hl ; 1 byte local READY READY: pop hl ; get the source address from the stack ld de,__PRGRAPH0 ; destination address ld bc,4 ; count ldir endp end asm end sub #endif

You see, the sub changes the Z80 code of <print.asm> in two positions. That's it. All I need for this to work with any future version of ZX BASIC (as long as <print.asm> is not deeply modified) is a label in <print.asm>. I could use other current more distant label instead, but that could break the module if <print.asm> is modified in the future.

Anyway I wonder if this addon be useful enough for other people.