1v13d/src/FxEngine/face.c

#include "face.h"

#define min(x,y) (x<y?x:y)
#define max(x,y) (x>y?x:y)
#define abs(x) (x>0?x:-x)

#include <stdbool.h>
static bool sens_horaire(FE_face const * face)
{
    int area = 0;

    area += face->s1->translated.x * face->s2->translated.y;
    area -= face->s2->translated.x * face->s1->translated.y;

    area += face->s2->translated.x * face->s3->translated.y;
    area -= face->s3->translated.x * face->s2->translated.y;

    area += face->s3->translated.x * face->s1->translated.y;
    area -= face->s1->translated.x * face->s3->translated.y;

    return (area < 0);
}

// gestion des lignes
typedef struct line line;
struct line
{
    int x,y,z;
    int dx,dy,dz;
    bool no_line; // si les deux points sont confondus
};

static void set_line(line* segment,FE_point const * s1, FE_point const * s2)
{
    segment->x=s1->translated.x;
    segment->y=s1->translated.y;
    segment->z=s1->translated.z;
    segment->dx=s2->translated.x-s1->translated.x;
    segment->dy=s2->translated.y-s1->translated.y;
    segment->dz=s2->translated.z-s1->translated.z;
    segment->no_line=(segment->dx==0&&segment->dy==0);
}

static bool get_x(int y, line const * segment, int * x)
{
    y-=segment->y;
    if (y<0 && segment->dy>0)
        return false;
    if (y>0 && segment->dy<0)
        return false;
    if (abs(y)>abs(segment->dy))
        return false;

    if (segment->dy!=0)
        *x=segment->x+(y*segment->dx)/segment->dy;
    else if (y==0)
        *x=segment->x+segment->dx;
    else
        return false;
    return  true;
}

#include "texture.h"
#include "zbuffer.h"
#include <gint/display.h>
void FE_draw_face(FE_face const * face)
{
    // élimination des faces cachées
    if (sens_horaire(face)!=face->visible)
        return;

    // cas particuliers où la face n'est pas dans l'écran
    if (face->s1->translated.x<0 && face->s2->translated.x<0 && face->s3->translated.x<0)
        return;
    if (face->s1->translated.x>127 && face->s2->translated.x>127 && face->s3->translated.x>127)
        return;
    if (face->s1->translated.y<0 && face->s2->translated.y<0 && face->s3->translated.y<0)
        return;
    if (face->s1->translated.y>63 && face->s2->translated.y>63 && face->s3->translated.y>63)
        return;
    if (face->s1->translated.z<=0 && face->s2->translated.z<=0 && face->s3->translated.z<=0)
        return;
    
    // cas où un côté est nul
    line cotes[3];
    set_line(&cotes[0], face->s1,face->s2);
    set_line(&cotes[1], face->s1,face->s3);
    set_line(&cotes[2], face->s2,face->s3);
    if (cotes[0].no_line || cotes[1].no_line || cotes[2].no_line)
        return;

    const int32_t y1 = max(min(face->s1->translated.y, min(face->s2->translated.y, face->s3->translated.y)), 0);
    const int32_t y2 = min(max(face->s1->translated.y, max(face->s2->translated.y, face->s3->translated.y)), 63);

    // ressources pour déformer les textures
    const int32_t   xAB = face->s2->translated.x-face->s1->translated.x, 
                    yAB = face->s2->translated.y-face->s1->translated.y, 
                    zAB=face->s2->translated.z-face->s1->translated.z;
    const int32_t   xAC = face->s3->translated.x-face->s1->translated.x, 
                    yAC = face->s3->translated.y-face->s1->translated.y, 
                    zAC=face->s3->translated.z-face->s1->translated.z;
    const int32_t diviseur_commun=(xAB*yAC-yAB*xAC);
    const int fact_1=(1024*yAC)/diviseur_commun, fact_2=(1024*xAC)/diviseur_commun;
    const int fact_3=(1024*xAB)/diviseur_commun, fact_4=(1024*yAB)/diviseur_commun;
    
    for (int y=y1; y<=y2; y++)
    {
        // détermination du xmin et du xmax de la ligne
        int tx1, tx2;
        for (int t=0;t<3;t++)
            if (get_x(y,&cotes[t],&tx1))
                break;
        for (int t=0;t<3;t++)
            if (get_x(y,&cotes[t],&tx2)&&tx1!=tx2)
                break;
        const int txmin=max(min(tx1,tx2),0), txmax=min(max(tx1,tx2),127);
        
        for (int x=txmin; x<=txmax; x++)
        {
            // vx et vy coordonnées transformées pour l'accès à la texture
            // z distance du point visible (distance non transformée)
            int32_t vx, vy, z;
            // calcul de vx, vy
            const int32_t xcalc = x-face->s1->translated.x, ycalc = y-face->s1->translated.y;
            vx=(xcalc*fact_1-ycalc*fact_2); // 0 <vx< 10_000 
            vy=(ycalc*fact_3-xcalc*fact_4); // idem

            z=face->s1->translated.z + (vx*zAB+vy*zAC)/1024; // calcul de z non corrigé >> fonctionnel
            if (z>0)
            {
                vx = (8 * vx * face->s1->translated.z) 
                                                      /
                                                       (1024 * face->s1->translated.z + (1024 - vx) * face->s2->translated.z);

                vy = (8 * vy * face->s1->translated.z) 
                                                      /
                                                       (1024 * face->s1->translated.z + (1024 - vy) * face->s3->translated.z);
    
                // Affichage du point
                if (FE_zbuffer_set_dist(x,y,z))
                    dpixel(x, y, 3*FE_get_pixel(face->texturenum, vx, vy)); // 3* means cast to black and white, and vx,and vy casted between 0 and 7
            }
        }
    }

// x=Det(AM,AC)/det(AB,AC) 
// y=det(AM,AB)/det(AC,AB)
    // x=(xAM*yAC-yAM*xAC)/(xAB*yAC-yAB*xAC)
    // y=(xAM*yAB-yAM*xAB)/(xAC*yAB-yAC*xAB)

    // soit diviseur_commun = (xAB*yAC-yAB*xAC)
    // x=xAM*yAC/diviseur_commun-yAM*xAC/diviseur_commun
    // y=yAM*xAB/diviseur_commun-xAM*yAB/diciseur_commun
}