asmhse / assembly-dos-gx

Assembly Graphics Demo for MS-DOS using TASM

Assembly DOS Graphics Library & Demo

This library + the demo I created can help students studying Computer Architecture in their Coursework. You can use it jusr for reference or use all of the Graphics macros and functions I created for you.

It was created for the TASM Assembler.

Demo

This is a simple demo, demonstrating the Usage of the Graphics and the Utilities Libraries. To compile and run it:

> tasm demo.asm
> tlink demo.obj
> demo.exe

TODO

• Adding line drawing function using Bresenham's line algorithm
• Adding circle drawing function using Bresenham's circle algorithm
• Border only / Filled shapes

Graphics Library

The graphics library has some neat macros and functions.

Macros

gx_set_video_mode mode

Sets the video mode to whatever mode specified.

Note: This macro uses the AX register.

Usage Example:

gx_set_video_mode 13h

---

gx_set_video_mode_gx

Sets the video mode 13h - 320x200 256 color graphics (MCGA,VGA).

Note: This macro uses the AX and ES registers.

Usage Example:

gx_set_video_mode_gx

---

gx_set_video_mode_txt

Sets the video mode 03h - 80x25 Monochrome text (MDA,HERC,EGA,VGA).

Note: This macro uses the AX register.

Usage Example:

gx_set_video_mode_txt

---

gx_pixel x, y, color

Sets a pixel using Video Memory. Relies upon having the Video Memory star address set in the ES register. Note that you don't have to do that if you initialised the Graphics mode using: gx_set_video_mode_gx and you haven't changed the value in the ES register.

_Note: This macro only works if you are using Graphics Mode 13h and you've initialised the graphics mode with the: gx_set_video_mode_gx macro.

Note: This macro uses the AX, BX and DI registers and Video Memory.

Usage Example:

gx_pixel 10, 10, 47 ; X: 10, Y: 10, Color: 47 (Green)

---

gx_pixel_bios x, y, color

Sets a pixel using the BIOS int 10h API.
This function is slower than gx_pixel so except in the cases where you must use a Graphics Mode different than 13h the usage if gx_pixel is recommended.

Note: This macro uses the AX, CX and DX registers.

Usage Example:

gx_pixel_bios 10, 10, 47 ; X: 10, Y: 10, Color: 47 (Green)

Functions

gx_rect

Draws a filled rectange between (x1;y1) and (x2;y2) Parameters:

• gx_x1
• gx_y1
• gx_x2
• gx_y2
• gx_color

Note: This function requires graphics mode 13h initalised with: gx_set_video_mode_gx.

Note: This function uses the AX, BX and DI registers and Video Memory.

Usage Example:

; To draw a Green Square, 10 pixels wide.
mov gx_x1, 10 ; X1 = 10
mov gx_y1, 10 ; Y1 = 10
mov gx_x2, 20 ; X2 = 20
mov gx_y2, 20 ; Y2 = 20
mov gx_color, 47 ; Color = 10
call gx_rect

Utilities Library

Macros

movv to, from

To move the content of one memory variable to another.

Usage Example:

movv gx_x1, gx_x2

---

cmpv var1, var2, register

Compares two memory variables using a register for temprary storage.

Usage Example:

cmpv gx_x1, gx_x2, ax ; Compares gx_x1 and gx_x2 using the AX register

---

addv to, from

Adds two memory variables.

Usage Example:

addv gx_x1, gx_x2, ax

---

subv to, from

Subtracts two memory variables.

Usage Example:

subv gx_x1, gx_x2, ax

---

return code

Returns control to DOS returning the specified in the first argument code.

Usage Example:

return 0

---

save_registers

Pushes AX, BX, CX and DX to the stack.
Can be later retrieved by: restore_registers.

Usage Example:

mov ax, 10
mov bx, 20
save_registers
mov ax, 30
mov bx, 50
restore_registers
; AX is now 10 and BX is now 20

---

restore_registers

Pops AX, BX, CX and DX from the stack.

See: save_registers.

Usage Example:

mov ax, 10
mov bx, 20
save_registers
mov ax, 30
mov bx, 50
restore_registers
; AX is now 10 and BX is now 20

Functions

check_keypress

Checks for a keypress. Sets ZF if no keypress is available. Otherwise returns it's scan code into AH and it's ASCII code into AL. Removes the character from the Type Ahead Buffer

Note: This function uses the AX register.

Usage Example:

start:

mainloop:
  call check_keypress
  jz render 	; No keypress available - skip other instructions and render a frame
	cmp al, 27 	; Check if ASCII code of the key is 27 (ESC)
	je exit		  ; If so exit the program
  
render:
  ; Some Graphics code
  jmp mainloop
  
exit:
  return 0

License

This library and it's supporting documentation are released under The MIT License (MIT).