mirror of
https://github.com/ekeeke/Genesis-Plus-GX.git
synced 2024-11-15 07:15:12 +01:00
90 lines
3.0 KiB
Plaintext
90 lines
3.0 KiB
Plaintext
|
|
||
|
|
Introduction
|
||
|
|
|
||
|
|
Genesis Plus has reasonable speed, and very fast rendering. Here are some
|
||
|
|
details about porting it to another platform
|
||
|
|
|
||
|
|
Porting rules
|
||
|
|
|
||
|
|
- This program is released under the GPL, so please release the source
|
||
|
|
code for your derivative ports. Let me know if you need an alternative
|
||
|
|
to this.
|
||
|
|
|
||
|
|
- Do not change the name of the emulator. Something like 'Genesis Plus / MacOS'
|
||
|
|
is fine as it keeps the original name.
|
||
|
|
|
||
|
|
- Configure the CPU emulators for little or big-endian CPUs, and use the
|
||
|
|
ALIGN_LONG option to handle unaligned memory accesses if needed. E.g. if
|
||
|
|
the emulator crashes when a game scrolls horizontally, you need to enable
|
||
|
|
it.
|
||
|
|
|
||
|
|
Requirements
|
||
|
|
|
||
|
|
- At this time the 16-bit rendering code has been well tested and should
|
||
|
|
be used. There is code to support 8 through 32-bit displays, but I
|
||
|
|
haven't checked if it still works.
|
||
|
|
|
||
|
|
- Audio output, if enabled, uses stereo 16-bit samples.
|
||
|
|
|
||
|
|
Functions to use:
|
||
|
|
|
||
|
|
int load_rom(char *filename);
|
||
|
|
|
||
|
|
Loads a game which can be in BIN, SMD or ZIP formats. It returns zero if
|
||
|
|
an error has occured.
|
||
|
|
|
||
|
|
void system_init(void);
|
||
|
|
|
||
|
|
Initializes the virtual Genesis console. Call this once during startup.
|
||
|
|
|
||
|
|
void audio_init(int rate);
|
||
|
|
|
||
|
|
Initialize the sound emulation part of the emulator. Pass zero or don't
|
||
|
|
call the function to disable sound. Call this after running system_init().
|
||
|
|
|
||
|
|
void system_reset(void);
|
||
|
|
|
||
|
|
Resets the virtual Genesis console. Call this once during setup, and later
|
||
|
|
as needed.
|
||
|
|
|
||
|
|
int system_frame(int skip);
|
||
|
|
|
||
|
|
Updates the emulation for a frame. Pass 1 to prevent rendering (which can
|
||
|
|
be used for frame skipping) and 0 to render the current display.
|
||
|
|
|
||
|
|
This function returns 0 if the virtual Genesis console has locked up.
|
||
|
|
You can do what you'd like with this information, such as notify the user,
|
||
|
|
reset the machine, etc.
|
||
|
|
|
||
|
|
If audio is enabled, the snd.buffer[] array will hold the current audio
|
||
|
|
data for this frame.
|
||
|
|
|
||
|
|
void system_shutdown(void);
|
||
|
|
|
||
|
|
Shuts down the emulator.
|
||
|
|
|
||
|
|
Variables:
|
||
|
|
|
||
|
|
The 'bitmap' structure needs to be filled out prior to calling system_init().
|
||
|
|
This provides the rendering code with information about the type of bitmap
|
||
|
|
it is rendering to. I would advise sticking with a 1024x512 16-bit bitmap:
|
||
|
|
|
||
|
|
memset(&bitmap, 0, sizeof(t_bitmap));
|
||
|
|
bitmap.width = 1024;
|
||
|
|
bitmap.height = 512;
|
||
|
|
bitmap.depth = 16;
|
||
|
|
bitmap.granularity = 2; /* Bytes per pixel */
|
||
|
|
bitmap.pitch = (bitmap.width * bitmap.granularity);
|
||
|
|
bitmap.data = (unsigned char *)bmp->pixels; /* Pointer to your bitmap */
|
||
|
|
bitmap.viewport.w = 256; /* Initial size of display on power-up (do not change) */
|
||
|
|
bitmap.viewport.h = 224;
|
||
|
|
bitmap.viewport.x = 0x20; /* Offset used for rendering (do not change) */
|
||
|
|
bitmap.viewport.y = 0x00;
|
||
|
|
bitmap.remap = 1;
|
||
|
|
|
||
|
|
The variable 'input.pad[0]' holds the button states for the first player
|
||
|
|
gamepad. Update this prior to calling system_frame(), and use the bitmasks
|
||
|
|
defined in system.h such as 'INPUT_UP', etc.
|
||
|
|
|
||
|
|
See the Windows/SDL and DOS drivers for examples.
|