Difference between revisions of "Input"
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jnz mainloop ;fall through if 0, do jump somewhere else if otherwise | jnz mainloop ;fall through if 0, do jump somewhere else if otherwise | ||
</syntaxhighlight> | </syntaxhighlight> | ||
| + | |||
| + | Sometimes your <code>AH</code> register does not contain <code>00h</code> at any given time. In that case <code>dec ax</code> will never trigger the zero flag, so you would have to spend the extra byte and use <code>dec al</code>. Alternatively you can redesign your codeflow as to have <code>00h</code> in <code>AH</code> at least sometimes ;) | ||
== Checking for '''any''' keypress == | == Checking for '''any''' keypress == | ||
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The above are somewhat flaky due to different hardware, VMs, and emulators not honoring flags correctly. | The above are somewhat flaky due to different hardware, VMs, and emulators not honoring flags correctly. | ||
| + | |||
| + | == The DOS alternative == | ||
| + | |||
| + | In very small productions, it's sometimes impossible to use one of the above, since <code>AL</code> contains intermediate results or pixel values all the time. Luckily there is <code>int 16h</code> which checks for any key with the following code : | ||
| + | |||
| + | <syntaxhighlight lang=nasm> | ||
| + | mov ah,1 ; subfunction AH = 1, check for key | ||
| + | int 16h | ||
| + | jz mainloop ; ZF set if no keystroke available | ||
| + | </syntaxhighlight> | ||
| + | |||
| + | See also : [http://www.ctyme.com/intr/rb-1755.htm Ralf Browns Interrupt List : Int 16/AH=01h] | ||
| + | |||
| + | == Reading the Mouse == | ||
| + | |||
| + | For more sophisticated interaction with the mouse, there is <code>int 33h</code>. The most important interactions : | ||
| + | |||
| + | * [http://www.ctyme.com/intr/rb-5957.htm show mouse cursor - Int 33/AX=0001h] | ||
| + | * [http://www.ctyme.com/intr/rb-5959.htm return position and button status - Int 33/AX=0003h] | ||
| + | * [http://www.ctyme.com/intr/int-33.htm general overview] | ||
| + | |||
| + | For a case study in putting this together in a tinyprog, [[Paint16b|a little "Paint" implementation]] is possible in 16 bytes. | ||
Latest revision as of 14:16, 14 August 2016
Contents
Checking for ESCAPE
This is fairly easy: Monitor the keyboard scancode port for ESC which is #1, then deal with it:
in al,60h ;read whatever is at keyboard port; looking for ESC which is #1
dec ax ;if ESC, AX now 0
jnz mainloop ;fall through if 0, do jump somewhere else if otherwise
Sometimes your AH register does not contain 00h at any given time. In that case dec ax will never trigger the zero flag, so you would have to spend the extra byte and use dec al. Alternatively you can redesign your codeflow as to have 00h in AH at least sometimes ;)
Checking for any keypress
If you need to shave a byte, it might be possible in some environments to check for any keypress instead of just escape using less code:
in al,60h ;read whatever is at keyboard port
das ;If non-zero, parity will be set
jp mainloop ;Jump if parity
An alternative if not running DOSBox:
in al,60h ;read whatever is at keyboard port
aaa
jz mainloop ;Jump if zero
The above are somewhat flaky due to different hardware, VMs, and emulators not honoring flags correctly.
The DOS alternative
In very small productions, it's sometimes impossible to use one of the above, since AL contains intermediate results or pixel values all the time. Luckily there is int 16h which checks for any key with the following code :
mov ah,1 ; subfunction AH = 1, check for key
int 16h
jz mainloop ; ZF set if no keystroke available
See also : Ralf Browns Interrupt List : Int 16/AH=01h
Reading the Mouse
For more sophisticated interaction with the mouse, there is int 33h. The most important interactions :
- show mouse cursor - Int 33/AX=0001h
- return position and button status - Int 33/AX=0003h
- general overview
For a case study in putting this together in a tinyprog, a little "Paint" implementation is possible in 16 bytes.
