source: soft/giet_vm/applications/raycast/disp.c

#include "disp.h"
#include "game.h"
#include <stdio.h>
#include <stdlib.h>
#include <malloc.h>
#include <math.h>
#include <hard_config.h>
#include <user_lock.h>

#define FIELD_OF_VIEW   (70.f * M_PI / 180.f)   // Camera field of view
#define TEX_SIZE        (32)                    // Texture size in pixels
#define CEILING_COLOR   (0xBB)                  // lite gray
#define FLOOR_COLOR     (0x33)                  // dark gray


////////////////////////////
// Extern variables
////////////////////////////

extern unsigned char*  g_tex[5];
extern unsigned char*  buf;
extern void*           sts;
extern unsigned int    slice_x;
extern unsigned int    slice_count;
extern sqt_lock_t      slice_get_lock;
extern sqt_lock_t      slice_done_lock;
extern Game            game;

//////////////////////
// Local functions
////////////////////////

/////////////////////////////////////////////////////////////////////////
static void dispDrawColumnTex(int x, int y0, int y1, unsigned char *line)
{
    int y = (y0 >= 0 ? y0 : 0);
    int ymax = (y1 < FBUF_Y_SIZE ? y1 : FBUF_Y_SIZE);

    for (; y < ymax; y++) 
    {
        // Find texture coordinate
        int ty = (y - y0) * TEX_SIZE / (y1 - y0);

        buf[y * FBUF_X_SIZE + x] = line[ty];
    }
}

///////////////////////////////////////////////////////////////////////////
static void dispDrawColumnSolid(int x, int y0, int y1, unsigned char color)
{
    int y = (y0 >= 0 ? y0 : 0);
    int ymax = (y1 < FBUF_Y_SIZE ? y1 : FBUF_Y_SIZE);

    for (; y < ymax; y++) 
    {
        buf[y * FBUF_X_SIZE + x] = color;
    }
}

////////////////////////////////////////////////////////////////
static void dispDrawSlice( int x, int height, int type, int tx )
{
    // Ceiling
    dispDrawColumnSolid(x,
                        0,
                        (FBUF_Y_SIZE - height) / 2,
                        CEILING_COLOR);

    // Wall
    unsigned char *tex = g_tex[type];

    if (tex) {
        // Draw a texture slice
        dispDrawColumnTex(x,
                          (FBUF_Y_SIZE - height) / 2,
                          (FBUF_Y_SIZE + height) / 2,
                          &tex[tx * TEX_SIZE]);
    }
    else {
        // Draw a solid color slice
        dispDrawColumnSolid(x,
                            (FBUF_Y_SIZE - height) / 2,
                            (FBUF_Y_SIZE + height) / 2,
                            0xFF);
    }

    // Floor
    dispDrawColumnSolid(x,
                        (FBUF_Y_SIZE + height) / 2,
                        FBUF_Y_SIZE,
                        FLOOR_COLOR);
}

///////////////////////////////////////////////////////////////////////
static float dispRaycast( int *type, float *tx, float angle )
{
    float x = game.player.x;
    float y = game.player.y;

    // Camera is inside a block.
    // Return a minimal distance to avoid a division by zero.
    if ((gameLocate(floor(x), floor(y))) != 0) {
        *type = 0;
        *tx = 0.f;
        return 0.0001f;
    }

    // Precompute
    float vsin = sin(angle);
    float vcos = cos(angle);
    float vtan = vsin / vcos;

    // Calculate increments
    int incix = (vcos > 0.f) - (vcos < 0.f);
    int inciy = (vsin > 0.f) - (vsin < 0.f);
    float incfx = inciy / vtan;
    float incfy = incix * vtan;

    // Calculate start position
    int ix = floor(x) + (incix > 0);
    int iy = floor(y) + (inciy > 0);
    float fx = x + incfx * fabs(floor(y) + (inciy > 0) - y);
    float fy = y + incfy * fabs(floor(x) + (incix > 0) - x);

    // Find the first colliding tile in each direction
    while (incix && gameLocate(ix - (incix < 0), fy) == 0)
    {
        ix += incix;
        fy += incfy;
    }
    while (inciy && gameLocate(fx, iy - (inciy < 0)) == 0)
    {
        fx += incfx;
        iy += inciy;
    }

    // Find the shortest ray
    float dx = (incix) ? ((ix - x) / vcos) : 0xFFFF;
    float dy = (inciy) ? ((iy - y) / vsin) : 0xFFFF;

    if (dx < dy)
    {
        // Get block type
        *type = gameLocate(ix - (incix < 0), floor(fy));

        // Get wall texture coordinate [0;1]
        *tx = fy - floor(fy);
        if (incix < 0)
            *tx = 1 - *tx;

        return dx;
    }
    else
    {
        // Get block type
        *type = gameLocate(floor(fx), iy - (inciy < 0));

        // Get wall texture coordinate [0;1]
        *tx = fx - floor(fx);
        if (inciy > 0)
            *tx = 1 - *tx;

        return dy;
    }
}

////////////////////////////////////////////////////////////////
static void dispTranspose(unsigned char *buf, unsigned int size)
{
    int i, j;
    unsigned char pixel;

    for (i = 0; i < size; i++) {
        for (j = i + 1; j < size; j++) {
            int ai = i * size + j;
            int bi = j * size + i;

            pixel = buf[ai];
            buf[ai] = buf[bi];
            buf[bi] = pixel;
        }
    }
}

////////////////////////
// Exported functions
////////////////////////

//////////////////////////////////////////
unsigned char* dispLoadTexture(char *path)
{
    int fd;
    unsigned char *tex;

    tex = malloc(TEX_SIZE * TEX_SIZE);
    fd = giet_fat_open(path, O_RDONLY);
    if (fd < 0) 
    {
        free(tex);
        return NULL;
    }

    giet_fat_read(fd, tex, TEX_SIZE * TEX_SIZE);
    giet_fat_close(fd);

    dispTranspose(tex, TEX_SIZE);

    return tex;
}

///////////////////////////////////////////////////
unsigned int dispRenderSlice( unsigned int* slice )
{
    // return 0 when there is no more slice to do

    int type;
    float angle, dist, tx;
    unsigned int x;

    // get a slice index 
    sqt_lock_acquire( &slice_get_lock );

    if (slice_x >= FBUF_X_SIZE)      // No more work to do for this frame
    {
        sqt_lock_release( &slice_get_lock );
        return 0;
    }
    else                             // Keep slice coordinate
    {
        x       = slice_x;
        slice_x = x + 1;
        sqt_lock_release( &slice_get_lock );
        *slice  = x;
    }

    // Cast a ray to get wall distance
    angle = game.player.dir - FIELD_OF_VIEW / 2.f +
            x * FIELD_OF_VIEW / FBUF_X_SIZE;

    dist = dispRaycast(&type, &tx, angle);

    dist *= cos(game.player.dir - angle);

    // Draw ceiling, wall and floor
    dispDrawSlice(x, FBUF_Y_SIZE / dist, type, tx * TEX_SIZE);

    // Signal this slice is done

    sqt_lock_acquire( &slice_done_lock );
    slice_count++;
    sqt_lock_release( &slice_done_lock );

    return 1;
}  // end dispRenderSlice()