Developing NES game (cc65) 03 and VRAM buffer with C language

Paste the CSDN The format is not adjusted , If you want to see a good format, click below

https://happysoul.github.io/nes/nesdoug/

 

I wrote some support functions to fill VRAM buffer .

 

I used some background scene code , stay crt0.s A is defined in VRAM_BUF, The address is $700.

Please note that , This is technically similar to C Stack sharing 700-7ff Space . They may conflict . If you are worried about this problem, please send VRAM The buffer is set to 600-6ff.

But you can't go to VRAM Buffer write exceeds 74 bytes, It won't be better than 77 bytes More .

C Stack from 7ff Start to grow . also ,C The stack only needs a dozen bytes , If you program like me , And do not use local variables , And pass only a few functions at a time （ Better not ）, And do not use recursion . If you do those things , You're going to be OK . however , I think I should let you know .

 

To use my system , You need some internal pointers to my system . There is no need to pass values , The address is from crt0.s Medium VRAM_BUF Definition .

 

set_vram_buffer()

 

It's a bit like set_vram_update().

To put PPU Update points to another dataset , You can use set_vram_update(&data)

Close to use set_vram_update(NULL)

 

Another thing you need to do is reset the buffer every frame .

clear_vram_buffer()

When you write to the buffer , It will remember its location , And will continue to grow .clear_vram_buffer() Will reset the index to zero .

Data is automatically transmitted between frames , So in ppu_wait_nmi() after , Data has been sent , We can clear it .

 

Buffer a single map

one_vram_buffer(tile, ppu_address)

 

You just need the tile number and address . This macro can get the address NTADR_A(x,y)

X and Y Is the tile position .X from 0 To 31,Y from 0 To 29.

 

You can also use the function I wrote to calculate the address at run time

Pixel point 0-255 X, 0-239 Y

NT yes nametable,0-3 （ remarks ： That is to say 4 Block screen ）

get_ppu_addr(char nt, char x, char y);

 

You can write a continuous run

multi_vram_buffer_horz(const char * data, unsigned char len, int ppu_address);

or

multi_vram_buffer_vert(const char * data, unsigned char len, int ppu_address);

Horz From left to right ,Vert From top to bottom

 

Address 、 data 、EOF Be copied to VRAM buffer , One of the advantages is , When the buffer is continuously written ,EOF Will automatically adjust .

 

But here is a problem that needs attention , The size of the buffer is not monitored , If you write too much carelessly （ Overflow buffer ）, There's going to be a problem （ Blurred screen 、 The statement 、 Not aligned 、 collapse ）

 

I wrote a lot of examples of writing screens , And these are all in one v-blank Completed during . This is almost the maximum amount you can change in a frame .

 

 

https://github.com/nesdoug/03_Hello3/blob/master/hello3.c

 

https://github.com/nesdoug/03_Hello3