- 1 year ago
When using win32 assembly, how do you get the state of a key?
In Win32 assembly, you can use the GetAsyncKeyState
function to determine the state of a key. Here's how you can use it:
Load the necessary libraries: In your assembly code, make sure to import the required libraries. You'll need to import
user32.dll
to access theGetAsyncKeyState
function. Here's an example:assemblyextern GetAsyncKeyState : proc
import user32.dll
Call the
GetAsyncKeyState
function: To check the state of a key, pass the virtual key code of the key you're interested in as an argument toGetAsyncKeyState
. The function returns a short integer that contains information about the key's state.assembly; Example code to get the state of the 'A' key (virtual key code 0x41)
push 0x41 ; Push the virtual key code onto the stack
call GetAsyncKeyState
add esp, 4 ; Clean up the stack after the function call
Interpret the result: The return value of
GetAsyncKeyState
is a short integer where the most significant bit (bit 15) indicates whether the key is currently pressed. You can use bitwise operators to extract this information. For example:assembly; Example code to check if the 'A' key is currently pressed
test ax, 0x8000 ; Test bit 15 (most significant bit)
jnz KeyPressed ; Jump to 'KeyPressed' label if the result is non-zero
; Key is not pressed
jmp KeyNotPressed
KeyPressed:
; Key is currently pressed
jmp Done
KeyNotPressed:
; Key is not currently pressed
jmp Done
Done:
; Continue with the rest of your code
This code snippet demonstrates how to check the state of the 'A' key using the GetAsyncKeyState
function in Win32 assembly. You can adapt it to check the state of other keys by changing the virtual key code in the push
instruction and updating the corresponding label names. Remember to handle the key states appropriately in your application logic.