Developing NES games with C language (cc65) 08. Background collision

There are some differences between the background and the spirit , We can't read PPU Bytes in .

Let's make a map first , The size of each block is 16x16, Filling the whole background requires 240 An array of bytes .X from 0-15,Y from 0-14. We put the array into RAM in , To prevent it from being modified .

The operation will be demonstrated later , First look at the array structure .

 

 

 

const unsigned char c2 [] = {

0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,

0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,

0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,

0,0,0,0,0,1,0,0,1,0,0,0,0,0,0,0,

0,0,0,0,0,1,0,0,1,0,0,0,0,0,0,0,

0,0,0,0,0,1,0,0,1,0,0,0,0,0,0,0,

0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,

0,0,0,1,0,0,0,0,0,0,1,0,0,0,0,0,

0,0,0,0,1,0,0,0,0,1,0,0,0,0,0,0,

0,0,0,0,0,1,1,1,1,0,0,0,0,0,0,0,

0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,

0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,

0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,

0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,

0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0

};

 

 

 

1 Represents a block in the game

 

 

To detect collisions , You just need to X and Y Remove the low byte of , Then put it together , Explain the method later

X>>4 take X Move right 4 position ,Y & 0xF0 take Y It's low 4 A into 0, Compare it with the values in the array one by one ,1 Collision ,0 No,

 

I will test the elves 4 A direction , And modify it during collision U D L R 4 Attribute values （ Is whether there is a collision in the up, down, left and right directions of the spirit ）

I'll do it first X Move , Check for collisions , If it collides, jump , Move again Y, Check for collisions , If it collides, skip , That is, do not move . Look at the function bg_collision()

 

This code should be streamlined , Because every frame will have XY The change of , I will modify the code to achieve speed change . Every frame 1 Pixels are too slow , It will cause a bad game experience .

 

I'm used to using Tiled Map Make game levels , It is very simple to use , And you can export csv file , This makes it easy to make C Array of . But this tool cannot import NES Format .chr file , So I have to redo all types of map blocks . It's very simple , We just need 2 A species , Blank blocks and ordinary map blocks .

 

Let me use it first. NES Screen Tool Make blocks , Then draw 2x2 The block . It seems that this approach is a little stupid , But when there are dozens of tiles in your game , It will be very happy 了

Because there is no way to export nametable Pictures of the , So I screenshot and then in GIMP edit , Save as metatile.png

With tileset How to import Tiled Map In the map editor . because nes Screen tools double pixels , So the size of each picture is 32x32

（ Translation notes ： It means that the screenshot image of the editor is relatively large , No 8x8 Of , It is 32x32 Of , That's why the above situation ）

Edit the level map , export csv file .

 

 

SV The file is converted to C Arrays are a small thing , But I still made a python3 Script to achieve . I will C Array import my code , Then use an array of pointers to point to the previous array .

 

 

 

#include “CSV/c1.c”

#include “CSV/c2.c”

#include “CSV/c3.c”

#include “CSV/c4.c”

 

const unsigned char * const All_Collision_Maps[] = {c1,c2,c3,c4};

 

 

 

Now? , I wrote some code , Will a 2×2 Block by block print to the screen , A big loop is used , It's used inside. vram_put() Method .

Use vram_put() You need to close the screen before , write in PPU So from left to right , Then the next line starts from left to right . In this way, you can easily write the whole screen .

 

Start Press the key to switch to the next map display

 

When you press right ,X The location will be +1, And then test 4 Collision points , If there is a collision, it will end moving to the right （X Meeting -1）

（ Translation notes ： The author uses The points after coordinate transformation are used to detect collision , In case of collision, it will retreat to change , If there is no collision , The spirit will move according to the changed point -- That is to redraw the new location of the spirit ）

 

test ： Hit the wall in the direction , Collision can take effect . Press Start Button , Background changes , The collision is still valid , because RAM Loaded a new map collision detection .

 

Be careful ： I moved the whole background down by scrolling the screen 1 Pixel .Y scroll=ff(-1), Because sprites always move down one pixel , Therefore, the background must be moved down as a whole 1 Pixel .

 

https://github.com/nesdoug/09_BG_Collide/blob/master/collide.c

 

https://github.com/nesdoug/09_BG_Collide

 

The code of the map loading part is not well written , Because you can only paint one kind of map block , And the property sheet will not be modified , Later I will introduce a better loading method （11、Metatiles）, Before that, let me talk about rolling .