Learn Multi platform 8086 Assembly Programming... For World Domination!

Simple Samples

In this series we'll look at simple tasks... each will be a single ASM file, and will compile into a usable example you can build on

Lesson S1 - Sprite drawing and Simple key movement in MS DOS
Lets learn how to create a sprite, and move it around the screen with the keyboard.
Dos_Keyboard.asm

Starting our program
Our program starts with the basic definitions of a SMALL program, and a STACK size.

We then use INT 10h to turn on the bitmap screen, we're using 256 color mode, so each pixel will be 1 byte

Drawing a sprite
We're going to move a 8x8 smiley around the screen
You can use my Akusprite Editor to create files in the valid format for the DOS screen. It's free and open source - so you have no excuse!

You can learn more about AkuSprite Editor here.
Our Sprite is included in the source code
We pass an X,Y pos in DH,DL
Each line is 320 pixels (320 bytes)... we move in 8x8 'blocks' so we multiply the Xpos by 8, and they Ypos by 320*8

We then add the screen base - 0A000h:0000h
We 'XOR' the sprite with the screen pixels... this 'inverts' the image on the screen, meaning if it's drawn twice to the same pixel position it will be removed the second time.

Key reading and moving the sprite
We define the starting position of the sprite, and show the starting smiley position with our showsprite routine.
We need to process the 4 directions.

We use INT 16h - Function 01 to read the keyboard, this returns NZ if a key is waiting in the key buffer.

if there is then first we remove the old sprite, then we use INT 16h - Function 00 to get the keycode in AH

If a direction key is pressed, we then check the current smiley position - if it's already at the edge of the screen, we can't move again, but if we can, we move in the pressed direction.

We repeat for all 4 directions Up, Down, Left and Right.
We then repeat for any future movements.

here we've used VGA, but we've also covered EGA and CGA in the platform specific series.


Lesson S2 - Sprite drawing and Simple key movement on the Wonderswan
Lets write a sprite moving example on the Wonderswan and Wonderswan color.

The wonderswan is 4 color, and the WSC is 16 color, so the examples will be different

Starting our program
When our program starts, we need to define a Stack pointer
next we need to enable the graphics screen.
We're using a tilemap mode.
The settings are slightly different on the Wonderswan Color
We need to set up a palette...

On the Wonderswan we define 8 greyshades, and select 4 for our palette

On the Wonderswan Color we define 16 colors for our palette

We'll clear the tilemap (at 0000:1000+) with tile 0
The tilemap is 32x32 tiles
We need to transfer our smiley sprite to VRAM.

The Vram address is 0000:2000 on the Wonderswan

The Vram address is 0000:4000 on the Wonderswan Color

Drawing a sprite
We're going to move a 8x8 smiley around the screen
You can use my Akusprite Editor to create files in the valid format for the DOS screen. It's free and open source - so you have no excuse!

You can learn more about AkuSprite Editor here.
Our Sprite is included in the source code
Lets define a tile on screen!

The tilenumber is passed in AL

We pass an X,Y pos in DH,DL

Each line of the tilemap is 32 tiles.. each tile is 2 bytes... the Tilemap base is 0000h:1000h

so our formula for the tile to change is 1000h + (Xpos * 2) + (Ypos * 64)

Pad reading and moving the sprite
We define the starting position of the sprite, and show the starting smiley position with our showsprite routine.

We need to process the 4 directions.

we select one of the 3 sets of controls (X-Pad, Y-Pad buttons) by writing to 0B5h with one of the top 4 bits set.

We then read from 0B5h to get the current state of those buttons in the bottom 4 bits.

if a key is pressed we first remove the old sprite

We check if each direction key is pressed, we then check the current smiley position - if it's already at the edge of the screen, we can't move again, but if we can, we move in the pressed direction.

We repeat for all 4 directions Up, Down, Left and Right.
We now draw the new sprite position, pause a moment and repeat.
You can learn more about key-reading on the wonderswan in this tutorial here... have fun!