Lesson 04

Simple Image Processing

A crash course on adding images to your applications.

And we're back. This is the third part of Lesson 04. You shouldn't be here if you haven't completed parts one and two, so you should probably do that now.

After that bit of a headache at the end of the last section, the next line should be a nice refresher. It's just the simple module definition that we have used in all of our other programs:

PSP_MODULE_INFO("Image Display Program", 0, 1, 1);

Again we will add some familiar code, our standard callbacks.

/* Exit callback */
int exit_callback(int arg1, int arg2, void *common) {
          sceKernelExitGame();
          return 0;
}

/* Callback thread */
int CallbackThread(SceSize args, void *argp) {
          int cbid;

          cbid = sceKernelCreateCallback("Exit Callback", exit_callback, NULL);
          sceKernelRegisterExitCallback(cbid);

          sceKernelSleepThreadCB();

          return 0;
}

/* Sets up the callback thread and returns its thread id */
int SetupCallbacks(void) {
          int thid = 0;

          thid = sceKernelCreateThread("update_thread", CallbackThread, 0x11, 0xFA0, 0, 0);
          if(thid >= 0) {
                    sceKernelStartThread(thid, 0, 0);
          }

          return thid;
}

Look familiar? Good.

Now we get to the good stuff; it's the start of our main() function.

int main() {
char buffer[200];
Image* ourImage;

Up to this point, all we have done with strings is display them on the screen through the use of printf(). That's fine and dandy, but it's about time we get a little more in depth about what a string actually is. Basically, in C a string is an array of characters. There isn't such a thing in C as "myString," it is really just 8 character variables placed next to each other in memory. So to allow us to create a string, we have to first allocate that memory, because as soon as we do anything else (define a variable or whatnot), the memory space next to that allocated space next to the string will be reserved and therefore our string won't be allow to extend into it. Well, it will, it's called a buffer overflow, but we're not concerned about that right now; just know that it's generally a bad thing and will freeze your PSP. So to define an array in C, you simply add on how large you want the array (of a given type) to be in brackets after the variable name. So, when we use the line char buffer[200], we are allocating a block in memory of 200 character variables. This is the maximum length that our string can be, 200 characters. There is a way to change the size, but that's beyond the scope of this tutorial.

The second line in our main() function defines a new variable named "ourImage" of datatype Image; it is actually more of a linked list, but don't worry about that for now. This Image datatype was defined in the graphics.h header file which we included. Everything that we do with it will be through the use of other functions in that graphics.h file. Aren't you glad we are using that file? Otherwise this program would have been a major headache.

Guess what? That completes the third part of the fourth lesson. We're chugging quite along so let's continue to part four.

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Lesson 04

Simple Image Processing

A crash course on adding images to your applications.