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