I think it's time to start learning
about sprites, don't you? 'What is a sprite?' you ask. Well, I would
think you already know, but just in case you don't, a sprite
is just an image on the screen (except the background, although
a sprite could be that big). Any character, coin, etc. on the screen
is a sprite.
Just as you saw with backgrounds in Day 4, a sprite must be in the proper format.
Again, a sprite can be from 8x8 up to 64x64 pixels. There can be
up to 128 sprites on the screen at a time. They can share one 256
color palette or there can be up to 16 different 16 color palettes
that a sprite can use.
As I mentioned in Day 4, I will
work exclusively with bitmaps. For this tutorial I have created
a sprite which is just a blue ball called blue_ball.bmp. Copy the
file to your gfx subdirectory and type:
gfx2gba -D -fsrc -pblue_ball.pal -t8 blue_ball.bmp
This will create two files:
blue_ball.pal.c, blue_ball.raw.c
Again, two arrays will be created. The palette will be blue_ball_Palette
and the image will be blue_ball_Bitmap.
For today's code we'll just display the sprite on the screen. Later
we'll work on moving it around the screen. (I hope that you all know what global
variables are.)
NOTE: You'll notice that when the ball is displayed on the
screen you see the white background that is part of the original
image. Later on when we cover alpha blending, you'll learn how to
show only the blue ball without the white background.
// The Main HAM Library
#include <mygba.h>
// Graphics Includes
#include "gfx/blue_ball.raw.c"
#include "gfx/blue_ball.pal.c"
// Global Variables
u8 theball; // Sprite object number of the ball
// Function: main()
int main()
{
// Initialize HAMlib
ham_Init();
// Setup the background mode
ham_SetBgMode(4);
// Initialize the sprite palette
ham_LoadObjPal((void*)blue_ball_Palette, 256);
// Create the sprite and store the object number
theball = ham_CreateObj((void*)blue_ball_Bitmap,0,2,
OBJ_MODE_NORMAL,1,0,0,0,0,0,0,110,50);
// Draw the sprite
ham_CopyObjToOAM();
// Infinite loop to keep the program running
while(1) {}
return 0;
} // End of main()
Code Explanation
u8 theball
A u8 is defined in mygba.h as an unsigned char.
Each object that is created in memory has an object number (from 0 to 127). For this example, there is just one sprite so I simply store the object number in theball. Later on I will use arrays for sprites because if the sprite rotates or
turns at all, it is easy to load the different frames into the array
and use this for animation. This may seem somewhat confusing so
I will explain it more when we do our first
project.
ham_SetBgMode(4)
For this example we'll use Mode 4 although it doesn't really matter.
Sprites are separate of BGMode except that there is less sprite
storage space in certain BG Modes. However, HAM handles the trouble
there, no matter what BGMode you are in. You'll just have less available
OBJ RAM in some modes.
theball = ham_CreateObj(...) ham_CreateObj is used to create a sprite in the HAM system and
return the reference index for further operations on the sprite.
It is not very difficult to understand but there is a lot of information
that you must pass to the function. The first thing is the array
associated with the image that you want to display. Next is the
size and shape of the object. Check the chart
to see what your choices are. In this case, I am using an 32x32
pixel image, so I pass it 0 and then 2. What this means is that
there are 4x4 8 pixel blocks. Think about that for a minute to make
sure you understand what I mean. (NOTE: Instead of passing 0,2 you could use OBJ_SIZE_32X32.) Next is the object mode. For now,
I am just using OBJ_MODE_NORMAL. Next is the color mode. For this
sprite I have one 256 color palette, so I pass it 1. Next is the
palette number. Because I am using color mode 1, you just pass it
0. If you were using 16 separate 16 color palettes, you would pass
it the palette number which corresponds to your image (0-15). Next
are mosaic, horizontal flipping and vertical flipping. I am not
using any of them, so they are all 0. Next is the priority of the
object, in this case it's 0. Finally you pass it the X and Y position
on the screen.
ham_CopyObjToOAM()
This function is used to load all of the objects to OAM. This basically
means it draws the objects.
Well, another small step today but a major concept to understand. Try creating your own sprite, convert the file with gfx2gba
and see if you can display it. If you want to be really creative, make the sprite a size other than 32x32 pixels and see if you can get it to show up properly.
Download
Code
NOTE: You may need to Right-click and choose Save As.
HAM Version 2.40 And Higher
Download All Files In One Zip: Day5_Sprites.zip
