/*

     File: GLTextureAtlasViewController.m

 Abstract: The GLTextureAtlasViewController class is a GLKViewController subclass that renders OpenGL scene. It demonstrates how to bind a texture atlas once, and draw multiple objects with different textures using one draw call.

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#import "GLTextureAtlasViewController.h"

#import "PVRTexture.h"

#define USE_4_BIT_PVR       0 //if 0 use 2-bit pvr

#define kAnimationSpeed     0.2 // (0, 1], the bigger the faster

#define NUM_COLS            4

#define NUM_ROWS            4

#define NUM_IMPOSTERS       40

#define CLAMP(min,x,max) (x < min ? min : (x > max ? max : x))

#define DegreeToRadian(x) ((x) * M_PI / 180.0f)

// get random float in [-1,1]

static inline float randf() { return (rand() % RAND_MAX) / (float)(RAND_MAX) * 2. - 1.; }

typedef struct particle {

    float x, y, z, t, v, tx, ty, tz;

    int c;

} particle;

particle butterflies[NUM_IMPOSTERS];

@interface GLTextureAtlasViewController ()

{

    GLint widthScaleIndex, frameCount; //to simulate the fly effect

    GLuint textureAtlas;

    PVRTexture *pvrTextureAtlas;

    Boolean init;

}

@property (strong, nonatomic) EAGLContext *context;

@end

@implementation GLTextureAtlasViewController

- (void)viewDidLoad

{

    [super viewDidLoad];

    self.context = [[EAGLContext alloc] initWithAPI:kEAGLRenderingAPIOpenGLES1];

    if (!self.context) {

        NSLog(@"Failed to create ES context");

    }

    GLKView *view = (GLKView *)self.view;

    view.context = self.context;

    [EAGLContext setCurrentContext:self.context];

    // load the texture atlas in the PVRTC format

    if (USE_4_BIT_PVR)

        [self loadPVRTexture:@"butterfly_4"];

    else //use 2-bit pvr

        [self loadPVRTexture:@"butterfly_2"];

    // precalc some random normals and velocities

    int i;

    for (i = 0; i < NUM_IMPOSTERS; i++) {

        float x = randf();

        float y = randf();

        float z = randf();

        if (fabs(x<0.1) && fabs(y<0.1)) {

            x += (x>0) ? 0.1 : -0.1;

            y += (y>0) ? 0.1 : -0.1;

        }

        float m = 1.0/sqrtf( (x*x) + (y*y) + (z*z) );

        butterflies[i].x = x*m;

        butterflies[i].y = y*m;

        butterflies[i].z = z*m;

        butterflies[i].t = 0;

        butterflies[i].v = randf()/2.; butterflies[i].v += (butterflies[i].v > 0) ? 0.1 : -0.1;

        butterflies[i].c = i % (NUM_ROWS*NUM_COLS);

    }

    // enable GL states

    glEnableClientState(GL_VERTEX_ARRAY);

    glEnableClientState(GL_TEXTURE_COORD_ARRAY);

    glEnable(GL_TEXTURE_2D);

    glEnable(GL_BLEND);

    glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);

}

- (void)loadPVRTexture:(NSString *)name

{

    glGenTextures(1, &textureAtlas);

    glBindTexture(GL_TEXTURE_2D, textureAtlas);

    // setup texture parameters

    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);

    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);

    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);

    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);

    pvrTextureAtlas = [PVRTexture pvrTextureWithContentsOfFile:[[NSBundle mainBundle] pathForResource:name ofType:@"pvr"]];

    [pvrTextureAtlas retain];

    if (pvrTextureAtlas == nil)

        NSLog(@"Failed to load %@.pvr", name);

    glBindTexture(GL_TEXTURE_2D, 0);

}

- (void)didReceiveMemoryWarning

{

    [super didReceiveMemoryWarning];

    // Dispose of any resources that can be recreated.

}

- (void)dealloc {

    // release the texture atlas

    if (textureAtlas) {

        glDeleteTextures(1, &textureAtlas);

        textureAtlas = 0;

    }

    [pvrTextureAtlas release];

    pvrTextureAtlas = nil;

    if ([EAGLContext currentContext] == self.context) {

        [EAGLContext setCurrentContext:nil];

    }

    self.context = nil;

    [super dealloc];

}

#pragma mark - GLKView and GLKViewController delegate methods

- (void)update

{

    glMatrixMode(GL_PROJECTION);

    glLoadIdentity();

    GLfloat fov = 60.0f, zNear = 0.1f, zFar = 1000.0f, aspect = 1.5f;

    GLfloat ymax = zNear * tanf(fov * M_PI / 360.0f);

    GLfloat ymin = -ymax;

    glFrustumf(ymin * aspect, ymax * aspect, ymin, ymax, zNear, zFar);

    glMatrixMode(GL_MODELVIEW);

}

int comp(const void *p1, const void *p2)

{

    float d = ((particle *)p1)->tz - ((particle *)p2)->tz;

    if (d < 0) return -1;

    if (d > 0) return 1;

    return (int)p1 - (int)p2;

}

- (void)glkView:(GLKView *)view drawInRect:(CGRect)rect

{

    GLint i = 0, j;

    static GLfloat s = 1, sz = 1;

    static GLfloat sanim = 0.001, szanim = 0.002;

    static GLfloat widthScale[8] = { 1, 0.8, 0.6, 0.4, 0.2, 0.1, 0.6, 0.8 };

    static GLfloat tex[NUM_COLS*NUM_ROWS][8];

    static GLushort indices_all[NUM_IMPOSTERS*6];

    glClearColor(0.7f, 0.9f, 0.6f, 1.0f);

    glClear(GL_COLOR_BUFFER_BIT);

    if (!init)

    {

        // compute texture coordinates of each cell

        for (i = 0; i < NUM_COLS*NUM_ROWS; i++)

        {

            GLint row = i / NUM_COLS; //y

            GLint col = i % NUM_COLS; //x

            GLfloat left, right, top, bottom;

            left    = col       * (1./NUM_COLS);

            right   = (col+1)   * (1./NUM_COLS);

            top     = row       * (1./NUM_ROWS);

            bottom  = (row+1)   * (1./NUM_ROWS);

            // the order of the texture coordinates is:

            //{left, bottom, right, bottom, left, top, right, top}

            tex[i][0] = tex[i][4] = left;

            tex[i][2] = tex[i][6] = right;

            tex[i][5] = tex[i][7] = top;

            tex[i][1] = tex[i][3] = bottom;

        }

        // build the index array

        for (i = 0; i < NUM_IMPOSTERS; i++)

        {

            // the first and last additional indices are added to create degenerated triangles

            // between consistent quads. for example, we use the compact index array 0123*34*4567

            // to draw quad 0123 and 4567 using one draw call

            indices_all[i*6] = i*4;

            for (j=0; j<4; j++)

                indices_all[i*6+j+1] = i*4+j;

            indices_all[i*6+5] = i*4+3;

        }

        init = YES;

    }

    // SW transform point to find z order

    for (i = 0; i < NUM_IMPOSTERS; i++)

    {

        float ax = DegreeToRadian(butterflies[i].x*butterflies[i].t);

        float ay = DegreeToRadian(butterflies[i].y*butterflies[i].t);

        float az = DegreeToRadian(butterflies[i].z*butterflies[i].t);

        float cosx = cosf(ax), sinx = sinf(ax);

        float cosy = cosf(ay), siny = sinf(ay);

        float cosz = cosf(az), sinz = sinf(az);

        float p1 = (sinz * butterflies[i].y + cosz * butterflies[i].x);

        float p2 = (cosy * butterflies[i].z + siny * p1);

        float p3 = (cosz * butterflies[i].y  - sinz * butterflies[i].x);

        butterflies[i].tx = cosy * p1 - siny * butterflies[i].z;

        butterflies[i].ty = sinx * p2 + cosx * p3;

        butterflies[i].tz = cosx * p2 - sinx * p3;

    }

    qsort(butterflies, NUM_IMPOSTERS, sizeof(particle), comp);

    // the interleaved array including position and texture coordinate data of all vertices

    // first position (3 floats) then tex coord (2 floats)

    // NOTE: we want every attribute to be 4-byte left aligned for best performance,

    // so if you use shorts (2 bytes), padding may be needed to achieve that.

    static GLfloat pos_tex_all[NUM_IMPOSTERS*4*(3+2)];

    // now update the interleaved data array

    for (i = 0; i < NUM_IMPOSTERS; i++)

    {

        // in order to batch the drawcalls into a single one,

        // we have to drop usage of glMatrix/glTranslate/glRotate/glScale,

        // and do the transformations ourselves.

        // rotation around z

        GLfloat rotzDegree = butterflies[i].z * butterflies[i].t;

        if (rotzDegree >= 60.0 || rotzDegree <= -60.0)

        {

            butterflies[i].v *= -1.0;

            rotzDegree = CLAMP(-60.0, rotzDegree, 60.0);

        }

        GLfloat rotz = DegreeToRadian(rotzDegree);

        // scale along x

        GLint ind = (i%2 == 0) ? widthScaleIndex : 7-widthScaleIndex; //add some noise

        // compute the transformation matrix

        GLKMatrix4 Tz   = GLKMatrix4MakeTranslation(0.0, 0.0, -2.0);

        GLKMatrix4 S    = GLKMatrix4MakeScale(widthScale[ind]*0.2, 0.2, 1.0);

        GLKMatrix4 T    = GLKMatrix4MakeTranslation(butterflies[i].tx*s, butterflies[i].ty*s, butterflies[i].tz*sz);

        GLKMatrix4 Rz   = GLKMatrix4MakeZRotation(rotz);

        GLKMatrix4 M = GLKMatrix4Multiply(S, Tz);

        M = GLKMatrix4Multiply(T, M);

        M = GLKMatrix4Multiply(Rz, M);

        // simple quad data

        // 4D homogeneous coordinates (x,y,z,1)

        GLfloat pos[] = {

            -1,-1,0,1,  1,-1,0,1,   -1,1,0,1,   1, 1,0,1,

        };

        // first, position

        GLint v;

        for (v=0; v<4; v++) {

            // apply the resulting transformation matrix on each vertex

            GLKVector4 vout = GLKMatrix4MultiplyVector4(M, GLKVector4MakeWithArray(pos+v*4));

            GLfloat *temp = pos_tex_all+i*20+v*5;

            for (int t=0; t<4; t++)

                temp[t] = vout.v[t];

        }

        // then, tex coord

        for (j=0; j<8; j++)

        {

            GLint n = i*20 + (j/2)*5 + 3+j%2;

            GLint c = butterflies[i].c;

            pos_tex_all[n] = tex[c][j];

        }

        butterflies[i].t += butterflies[i].v;

    }

    // bind the texture atlas ONCE

    glBindTexture(GL_TEXTURE_2D, textureAtlas);

    glVertexPointer(3, GL_FLOAT, 5*sizeof(GLfloat), pos_tex_all);

    glTexCoordPointer(2, GL_FLOAT, 5*sizeof(GLfloat), pos_tex_all+3);

    // draw all butterflies using ONE single call

    glDrawElements(GL_TRIANGLE_STRIP, NUM_IMPOSTERS*6, GL_UNSIGNED_SHORT, indices_all);

    glBindTexture(GL_TEXTURE_2D, 0);

    // update parameters

    s += sanim;

    if ((s >= 1.5) || (s <= 1.0)) sanim *= -1.0;

    sz += szanim;

    if ((sz >= 1.4) || (sz <= -1.2)) szanim *= -1.0;

    GLfloat speed = CLAMP(0, kAnimationSpeed, 1);

    if (speed) {

        GLint speedInv = 1./speed;

        if (frameCount % speedInv == 0) {

            // update width scale to simulate the fly effect

            widthScaleIndex = widthScaleIndex < 7 ? widthScaleIndex+1 : 0;

        }

        frameCount ++;

    }

}

@end