mirror of
https://github.com/sehugg/8bitworkshop.git
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109 lines
3.1 KiB
C
109 lines
3.1 KiB
C
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/*
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Physics demo for Game Boy.
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A single sprite with velocity and friction, using fixed-point
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coordinates: positions are 16-bit values where the lower 4 bits
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are the sub-pixel fraction, dropped with >> 4 when the sprite
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is moved. Arrow keys apply thrust; holding A gives a jump burst.
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*/
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#include <stdint.h>
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#include <string.h>
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#include "gb/types.h"
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#include "gb/hardware.h"
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#include "gb/gb.h"
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// A simple sub-pixel / fixed point example
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// Postion values are calculated as 16 bit numbers and their
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// lower 4 bits are dropped when applying them to the sprite
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// 4 frames of a ball sprite (8x8, 1bpp)
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UINT8 sprite_data[] = {
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/*;;{w:8,h:8,bpp:1,count:4,brev:1,np:2,pofs:1,sl:2};;*/
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0x3C,0x3C,0x42,0x7E,0x99,0xFF,0xA9,0xFF,0x89,0xFF,0x89,0xFF,0x42,0x7E,0x3C,0x3C,
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0x3C,0x3C,0x42,0x7E,0xB9,0xFF,0x89,0xFF,0x91,0xFF,0xB9,0xFF,0x42,0x7E,0x3C,0x3C,
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0x3C,0x3C,0x42,0x7E,0x99,0xFF,0x89,0xFF,0x99,0xFF,0x89,0xFF,0x5A,0x7E,0x3C,0x3C,
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0x3C,0x3C,0x42,0x7E,0xA9,0xFF,0xA9,0xFF,0xB9,0xFF,0x89,0xFF,0x42,0x7E,0x3C,0x3C
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/*;;*/
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};
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joypads_t joypads;
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// fixed-point sprite coords (fraction in lower 4 bits)
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UINT16 PosX, PosY; // position
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INT16 SpdX, SpdY; // velocity
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UINT8 Jump; // frames of jump thrust remaining
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// main function
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void main(void) {
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// init palettes
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BGP_REG = OBP0_REG = OBP1_REG = 0xE4;
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// load tile data into VRAM
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set_sprite_data(0, 4, sprite_data);
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// set sprite tile
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set_sprite_tile(0, 0);
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// show bkg and sprites
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SHOW_BKG; SHOW_SPRITES;
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// init 2 joypads
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joypad_init(1, &joypads);
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// start at screen center with zero velocity
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PosX = PosY = 64 << 4;
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Jump = SpdX = SpdY = 0;
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// loop forever
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while(1) {
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// poll joypads
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joypad_ex(&joypads);
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// game object: arrow keys apply thrust, clamped to a max speed
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if (joypads.joy0 & J_UP) {
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SpdY -= 2;
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if (SpdY < -64) SpdY = -64;
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} else if (joypads.joy0 & J_DOWN) {
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SpdY += 2;
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if (SpdY > 64) SpdY = 64;
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}
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if (joypads.joy0 & J_LEFT) {
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SpdX -= 2;
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if (SpdX < -64) SpdX = -64;
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} else if (joypads.joy0 & J_RIGHT) {
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SpdX += 2;
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if (SpdX > 64) SpdX = 64;
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}
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// A button triggers a 3-frame jump (only when grounded)
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if ((joypads.joy0 & J_A) && (!Jump)) {
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Jump = 3;
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}
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// jump: apply upward impulse while Jump counts down
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if (Jump) {
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SpdY -= 8;
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if (SpdY < -32) SpdY = -32;
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Jump--;
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}
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// apply velocity to position
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PosX += SpdX, PosY += SpdY;
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// Translate to pixels and move sprite
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// Downshift by 4 bits to use the whole number values
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move_sprite(0, PosX >> 4, PosY >> 4);
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// friction: velocities decay toward zero each frame
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if (SpdY >= 0) {
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if (SpdY) SpdY--;
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} else SpdY ++;
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if (SpdX >= 0) {
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if (SpdX) SpdX--;
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} else SpdX ++;
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// Done processing, yield CPU and wait for start of next frame (VBlank)
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wait_vbl_done();
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}
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}
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