How to change the resolution of the screen (number of pixels) on a project in assembly language (DOSBox)

Question

Actually I am making a project in assembly language where I am printing mountains, sea, and soil on assembly language display memory. I just want to make my movements smooth or my resolution higher so that my pixels would be more clear. I want my 80x25 screen changed into a bigger one to increase resolution. Somewhat near 800 or 1280.

I have tried using int 10h services. I have used functions 01h, 06h and all related stuff but nothing changed at all.

Answer 1

DOSBox (current version 0.74) has VESA functionality, provided the options file has the required settings. Some of the settings in my options file are:

[sdl]
fullscreen=false
fulldouble=false
fullresolution=desktop
windowresolution=1280x960
output=openglnb

[dosbox]
machine=svga_s3

[render]
aspect=true
scaler=normal2x

I wrote this little demo to prove that it works:

  org  256

  mov  bx, 4115h        ; 32-bit 800x600 graphics
  mov  ax, 4F02h        ; VESA.SetVideoMode
  int  10h              ; -> AX
  cmp  ax, 004Fh
  jne  Abort
  call DrawDiagonals
  mov  ah, 00h          ; BIOS.GetKeystroke
  int  16h              ; -> AX
  mov  ax, 0003h        ; BIOS.SetVideoMode 80x25 text
  int  10h
Abort:
  mov  ax, 4C00h        ; DOS.Terminate
  int  21h
; ----------------------
DrawDiagonals:
  mov  cx, 600
  xor  eax, eax
  mov  ebx, 3200-4
.a:
  mov  dword [0C0000000h+eax], 004080C0h    ; 0RGB
  mov  dword [0C0000000h+ebx], 00C08040h    ; 0RGB
  add  eax, 3200+4
  add  ebx, 3200-4
  loop .a
  ret
; ----------------------

In a full-fledged application you would first ask VESA for its list with supported video modes, and then pick one for which you retrieve the characteristics (like LinearFrameBuffer address, BytesPerScanline, ...).
Consult the VESA documentation.