In this project, you're going to be developing a graphics engine in C. This graphics library will be writing directly to video memory, similar to the assembly-language graphics projects we've done in previous homeworks.
The code in this project runs on the bare metal with no operating system, so you
won't have standard features available like printf. I have included some basic
functions in stage1main.c and clibfuncs.c which you can call. In particular,
there is a function called setPixel that draws a pixel on the screen at a
given (x,y) coordinate.
Your job in this activity is to write some functions that draw things on the screen.
This function draws a line on the screen. You can use Bresenham's Line Algorithm to figure out which pixels need to be filled in. Refer to the Wikipedia article the get pseudocode for the algorithm, which you can translate into C.
Games like Mario, Pac Man, etc. draw images called sprites on the screen. The Mario character, for example, is a fixed image that the game draws at an arbitrary (x,y) location on the screen. When the user presses a key, the game changes the character's location accordingly and redraws the sprite. Bit blit (short for bit block transfer) is the method the game uses to copy the image of the character to the video buffer.
The BIOS has a special pallette of 256 colors that it can draw. If you want to draw a sprite on the screen, you need to make sure that the sprite is represented in the right color pallette. You can do this within Photoshop.
- Download the BIOS color pallette
- Open an image in Photoshop.
- Go to Image > Mode > Indexed Color... and under the Palette dropdown select Custom... Choose the palette file that you downloaded in step 1.
- Save the file as a jpeg or something.
- Use an online converter to convert the image into a C array.
- Paste the C array into a C file and compile it. If you create a new C file,
you'll need to add it to the
OBJSlist in the Makefile.
You need to copy the image from the C array into video memory one line at a time.