[HPX-dev] spec prelim-1

[Ian S. <ia...@st...>]

Specification for Project HPX Preliminary Phase I
=================================================

1.1 Aim

- start the project with some solid code
- understand how to use OpenGL to do simple 2D graphics

1.2 Summary

Display a background, then display an image according to a grid position on
the screen.

1.3 Use case

A sample run would proceed something like:
- switch mode to 640x480
- clear screen
- load RGB (24 bit) background image from file
- load RGBA (32 bit) "sprite" image from file(s)
- place background image into frame buffer
- place sprite image into frame buffer according to given (x,y) position
- swap frame buffer on to screen
- quit when esc is pressed

Note:
  RGB image == 1 byte for each of red, green, blue per pixel.
  RGBA image == 1 byte for each of red, green, blue, alpha per pixel, where
alpha designates % transparency

2.1 Code structure

Since we are moving towards a bomberman game, for this phase we want to
start coding in such a way as to allow us to build on the code as we
progress.

What I propose is to seperate the code into grid, object, display and main.

main.c
- contains the main() function and executes the functions provided by the
other files

display.c + display.h
- a simple display library which provides functions to load and display
different image formats

object.c + object.h
- contains definition of an object structure as well as functions that
manipulate objects. Each object need to have an associated image and current
location in x, y

grid.c + grid.h
- contains definition of the background grid structure and functions that
manipulate grids (or maps). Each map will need an associated background
image, grid width, grid height, tile width, tile height.

2.2 Detailed specification

2.2.1 display.h

Structures
- image structure
    - image width
    - image height
    - image data
    - image type

Functions
- loadBMP
    - read a 24 bit .bmp or .dib file and returns an image structure of type
RGB

- loadBMPAlpha
    - read a 24 bit .bmp or .dib and an 8 bit grayscale .bmp file and create
an image structure of type RGBA

- displayImage
    - places an image according to given x, y co-ordinates into the frame
buffer

2.2.2 object.h

Structures
- object structure
    - position x
    - position y
    - object RGBA image file(s?)

Functions
- displayObject
    - using the displayImage function displays the object at the correct
position

2.2.3 grid.h

Structures
- grid structure
    - overall background image
    - background width
    - background height
    - grid column count
    - grid row count

Functions
- displayGrid
    - displays the grid

3 Task allocation

Undecided. Everybody interested reply to this e-mail.

4 Unresolved problems
- how to create RGBA image data? I haven't figured this out yet
- how does the co-ordinate system work? OpenGL has a weird system whereby
the center of the screen is (0,0) and the corners are (-1, -1), (-1, 1), (1,
1) and (1, -1).
- is it probably better using a tiles system instead of 1 big background
where each tile has associated images  and each grid is an array of tiles?
Maybe we'll change to this later.