bbutil.c

/*
 * Copyright (c) 2011-2013 Research In Motion Limited.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
#include <ctype.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/keycodes.h>
#include <time.h>
#include <stdbool.h>
#include <math.h>

#include "bbutil.h"

#ifdef USING_GL11
#include <GLES/gl.h>
#include <GLES/glext.h>
#elif defined(USING_GL20)
#include <GLES2/gl2.h>
#else
#error bbutil must be compiled with either USING_GL11 or USING_GL20 flags
#endif

#include <ft2build.h>
#include FT_FREETYPE_H

#include "png.h"

EGLDisplay egl_disp;
EGLSurface egl_surf;

static EGLConfig egl_conf;
static EGLContext egl_ctx;

static screen_context_t screen_ctx;
static screen_window_t screen_win;
static screen_display_t screen_disp;
static int nbuffers = 2;
static int initialized = 0;

#ifdef USING_GL20
static GLuint text_rendering_program;
static int text_program_initialized = 0;
static GLint positionLoc;
static GLint texcoordLoc;
static GLint textureLoc;
static GLint colorLoc;
#endif

struct font_t {
    unsigned int font_texture;
    float pt;
    float advance[128];
    float width[128];
    float height[128];
    float tex_x1[128];
    float tex_x2[128];
    float tex_y1[128];
    float tex_y2[128];
    float offset_x[128];
    float offset_y[128];
    int initialized;
};


static void
bbutil_egl_perror(const char *msg) {
    static const char *errmsg[] = {
        "function succeeded",
        "EGL is not initialized, or could not be initialized, for the specified display",
        "cannot access a requested resource",
        "failed to allocate resources for the requested operation",
        "an unrecognized attribute or attribute value was passed in an attribute list",
        "an EGLConfig argument does not name a valid EGLConfig",
        "an EGLContext argument does not name a valid EGLContext",
        "the current surface of the calling thread is no longer valid",
        "an EGLDisplay argument does not name a valid EGLDisplay",
        "arguments are inconsistent",
        "an EGLNativePixmapType argument does not refer to a valid native pixmap",
        "an EGLNativeWindowType argument does not refer to a valid native window",
        "one or more argument values are invalid",
        "an EGLSurface argument does not name a valid surface configured for rendering",
        "a power management event has occurred",
        "unknown error code"
    };

    int message_index = eglGetError() - EGL_SUCCESS;

    if (message_index < 0 || message_index > 14)
        message_index = 15;

    fprintf(stderr, "%s: %s\n", msg, errmsg[message_index]);
}

/**
 * Use the PID to set the window group id.
 */
static const char *
get_window_group_id()
{
    static char s_window_group_id[16] = "";

    if (s_window_group_id[0] == '\0') {
        snprintf(s_window_group_id, sizeof(s_window_group_id), "%d", getpid());
    }

    return s_window_group_id;
}

int
bbutil_init_egl(screen_context_t ctx) {
    int usage;
    int format = SCREEN_FORMAT_RGBX8888;
    EGLint interval = 1;
    int rc, num_configs;

    EGLint attrib_list[]= { EGL_RED_SIZE,        8,
                            EGL_GREEN_SIZE,      8,
                            EGL_BLUE_SIZE,       8,
                            EGL_SURFACE_TYPE,    EGL_WINDOW_BIT,
                            EGL_RENDERABLE_TYPE, 0,
                            EGL_NONE};

#ifdef USING_GL11
    usage = SCREEN_USAGE_OPENGL_ES1 | SCREEN_USAGE_ROTATION;
    attrib_list[9] = EGL_OPENGL_ES_BIT;
#elif defined(USING_GL20)
    usage = SCREEN_USAGE_OPENGL_ES2 | SCREEN_USAGE_ROTATION;
    attrib_list[9] = EGL_OPENGL_ES2_BIT;
    EGLint attributes[] = { EGL_CONTEXT_CLIENT_VERSION, 2, EGL_NONE };
#else
    fprintf(stderr, "bbutil should be compiled with either USING_GL11 or USING_GL20 -D flags\n");
    return EXIT_FAILURE;
#endif

    //Simple egl initialization
    screen_ctx = ctx;

    egl_disp = eglGetDisplay(EGL_DEFAULT_DISPLAY);
    if (egl_disp == EGL_NO_DISPLAY) {
        bbutil_egl_perror("eglGetDisplay");
        bbutil_terminate();
        return EXIT_FAILURE;
    }

    rc = eglInitialize(egl_disp, NULL, NULL);
    if (rc != EGL_TRUE) {
        bbutil_egl_perror("eglInitialize");
        bbutil_terminate();
        return EXIT_FAILURE;
    }

    rc = eglBindAPI(EGL_OPENGL_ES_API);

    if (rc != EGL_TRUE) {
        bbutil_egl_perror("eglBindApi");
        bbutil_terminate();
        return EXIT_FAILURE;
    }

    if(!eglChooseConfig(egl_disp, attrib_list, &egl_conf, 1, &num_configs)) {
        bbutil_terminate();
        return EXIT_FAILURE;
    }

#ifdef USING_GL20
        egl_ctx = eglCreateContext(egl_disp, egl_conf, EGL_NO_CONTEXT, attributes);
#elif defined(USING_GL11)
        egl_ctx = eglCreateContext(egl_disp, egl_conf, EGL_NO_CONTEXT, NULL);
#endif

    if (egl_ctx == EGL_NO_CONTEXT) {
        bbutil_egl_perror("eglCreateContext");
        bbutil_terminate();
        return EXIT_FAILURE;
    }

    rc = screen_create_window(&screen_win, screen_ctx);
    if (rc) {
        perror("screen_create_window");
        bbutil_terminate();
        return EXIT_FAILURE;
    }

    rc = screen_create_window_group(screen_win, get_window_group_id());
    if (rc) {
        perror("screen_create_window_group");
        bbutil_terminate();
        return EXIT_FAILURE;
    }

    rc = screen_set_window_property_iv(screen_win, SCREEN_PROPERTY_FORMAT, &format);
    if (rc) {
        perror("screen_set_window_property_iv(SCREEN_PROPERTY_FORMAT)");
        bbutil_terminate();
        return EXIT_FAILURE;
    }

    rc = screen_set_window_property_iv(screen_win, SCREEN_PROPERTY_USAGE, &usage);
    if (rc) {
        perror("screen_set_window_property_iv(SCREEN_PROPERTY_USAGE)");
        bbutil_terminate();
        return EXIT_FAILURE;
    }

    rc = screen_get_window_property_pv(screen_win, SCREEN_PROPERTY_DISPLAY, (void **)&screen_disp);
    if (rc) {
        perror("screen_get_window_property_pv");
        bbutil_terminate();
        return EXIT_FAILURE;
    }

    const char *env = getenv("WIDTH");

    if (0 == env) {
        perror("failed getenv for WIDTH");
        bbutil_terminate();
        return EXIT_FAILURE;
    }

    int width = atoi(env);

    env = getenv("HEIGHT");

    if (0 == env) {
        perror("failed getenv for HEIGHT");
        bbutil_terminate();
        return EXIT_FAILURE;
    }

    int height = atoi(env);
    int size[2] = { width, height };

    rc = screen_set_window_property_iv(screen_win, SCREEN_PROPERTY_BUFFER_SIZE, size);
    if (rc) {
        perror("screen_set_window_property_iv");
        bbutil_terminate();
        return EXIT_FAILURE;
    }

    rc = screen_create_window_buffers(screen_win, nbuffers);
    if (rc) {
        perror("screen_create_window_buffers");
        bbutil_terminate();
        return EXIT_FAILURE;
    }

    egl_surf = eglCreateWindowSurface(egl_disp, egl_conf, screen_win, NULL);
    if (egl_surf == EGL_NO_SURFACE) {
        bbutil_egl_perror("eglCreateWindowSurface");
        bbutil_terminate();
        return EXIT_FAILURE;
    }

    rc = eglMakeCurrent(egl_disp, egl_surf, egl_surf, egl_ctx);
    if (rc != EGL_TRUE) {
        bbutil_egl_perror("eglMakeCurrent");
        bbutil_terminate();
        return EXIT_FAILURE;
    }

    rc = eglSwapInterval(egl_disp, interval);
    if (rc != EGL_TRUE) {
        bbutil_egl_perror("eglSwapInterval");
        bbutil_terminate();
        return EXIT_FAILURE;
    }

    initialized = 1;

    return EXIT_SUCCESS;
}

void
bbutil_terminate() {
    //Typical EGL cleanup
    if (egl_disp != EGL_NO_DISPLAY) {
        eglMakeCurrent(egl_disp, EGL_NO_SURFACE, EGL_NO_SURFACE, EGL_NO_CONTEXT);
        if (egl_surf != EGL_NO_SURFACE) {
            eglDestroySurface(egl_disp, egl_surf);
            egl_surf = EGL_NO_SURFACE;
        }
        if (egl_ctx != EGL_NO_CONTEXT) {
            eglDestroyContext(egl_disp, egl_ctx);
            egl_ctx = EGL_NO_CONTEXT;
        }
        if (screen_win != NULL) {
            screen_destroy_window(screen_win);
            screen_win = NULL;
        }
        eglTerminate(egl_disp);
        egl_disp = EGL_NO_DISPLAY;
    }
    eglReleaseThread();

    initialized = 0;
}

void
bbutil_swap() {
    int rc = eglSwapBuffers(egl_disp, egl_surf);
    if (rc != EGL_TRUE) {
        bbutil_egl_perror("eglSwapBuffers");
    }
}

/* Finds the next power of 2 */
static inline int
nextp2(int x)
{
    int val = 1;
    while(val < x) val <<= 1;
    return val;
}

font_t* bbutil_load_font(const char* path, int point_size, int dpi) {
    FT_Library library;
    FT_Face face;
    int c;
    int i, j;
    font_t* font;

    if (!initialized) {
        fprintf(stderr, "EGL has not been initialized\n");
        return NULL;
    }

    if (!path){
        fprintf(stderr, "Invalid path to font file\n");
        return NULL;
    }

    if(FT_Init_FreeType(&library)) {
        fprintf(stderr, "Error loading Freetype library\n");
        return NULL;
    }
    if (FT_New_Face(library, path,0,&face)) {
        fprintf(stderr, "Error loading font %s\n", path);
        return NULL;
    }

    if(FT_Set_Char_Size ( face, point_size * 64, point_size * 64, dpi, dpi)) {
        fprintf(stderr, "Error initializing character parameters\n");
        return NULL;
    }

    font = (font_t*) malloc(sizeof(font_t));

    if (!font) {
        fprintf(stderr, "Unable to allocate memory for font structure\n");
        return NULL;
    }

    font->initialized = 0;
    font->pt = point_size;

    glGenTextures(1, &(font->font_texture));

    //Let each glyph reside in 32x32 section of the font texture
    int segment_size_x = 0, segment_size_y = 0;
    int num_segments_x = 16;
    int num_segments_y = 8;

    FT_GlyphSlot slot;
    FT_Bitmap bmp;
    int glyph_width, glyph_height;

    //First calculate the max width and height of a character in a passed font
    for(c = 0; c < 128; c++) {
        if(FT_Load_Char(face, c, FT_LOAD_RENDER)) {
            fprintf(stderr, "FT_Load_Char failed\n");
            free(font);
            return NULL;
        }

        slot = face->glyph;
        bmp = slot->bitmap;

        glyph_width = bmp.width;
        glyph_height = bmp.rows;

        if (glyph_width > segment_size_x) {
            segment_size_x = glyph_width;
        }

        if (glyph_height > segment_size_y) {
            segment_size_y = glyph_height;
        }
    }

    int font_tex_width = nextp2(num_segments_x * segment_size_x);
    int font_tex_height = nextp2(num_segments_y * segment_size_y);

    int bitmap_offset_x = 0, bitmap_offset_y = 0;

    GLubyte* font_texture_data = (GLubyte*) calloc(2 * font_tex_width * font_tex_height, sizeof(GLubyte));

    if (!font_texture_data) {
        fprintf(stderr, "Failed to allocate memory for font texture\n");
        free(font);
        return NULL;
    }

    // Fill font texture bitmap with individual bmp data and record appropriate size, texture coordinates and offsets for every glyph
    for(c = 0; c < 128; c++) {
        if(FT_Load_Char(face, c, FT_LOAD_RENDER)) {
            fprintf(stderr, "FT_Load_Char failed\n");
            free(font);
            return NULL;
        }

        slot = face->glyph;
        bmp = slot->bitmap;

        glyph_width = bmp.width;
        glyph_height = bmp.rows;

        div_t temp = div(c, num_segments_x);

        bitmap_offset_x = segment_size_x * temp.rem;
        bitmap_offset_y = segment_size_y * temp.quot;

        for (j = 0; j < glyph_height; j++) {
            for (i = 0; i < glyph_width; i++) {
                font_texture_data[2 * ((bitmap_offset_x + i) + (j + bitmap_offset_y) * font_tex_width) + 0] =
                font_texture_data[2 * ((bitmap_offset_x + i) + (j + bitmap_offset_y) * font_tex_width) + 1] =
                    (i >= bmp.width || j >= bmp.rows)? 0 : bmp.buffer[i + bmp.width * j];
            }
        }

        font->advance[c] = (float)(slot->advance.x >> 6);
        font->tex_x1[c] = (float)bitmap_offset_x / (float) font_tex_width;
        font->tex_x2[c] = (float)(bitmap_offset_x + bmp.width) / (float)font_tex_width;
        font->tex_y1[c] = (float)bitmap_offset_y / (float) font_tex_height;
        font->tex_y2[c] = (float)(bitmap_offset_y + bmp.rows) / (float)font_tex_height;
        font->width[c] = bmp.width;
        font->height[c] = bmp.rows;
        font->offset_x[c] = (float)slot->bitmap_left;
        font->offset_y[c] =  (float)((slot->metrics.horiBearingY-face->glyph->metrics.height) >> 6);
    }

    glBindTexture(GL_TEXTURE_2D, font->font_texture);
    glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MAG_FILTER,GL_LINEAR);
    glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MIN_FILTER,GL_LINEAR);

    glTexImage2D(GL_TEXTURE_2D, 0, GL_LUMINANCE_ALPHA, font_tex_width, font_tex_height, 0, GL_LUMINANCE_ALPHA , GL_UNSIGNED_BYTE, font_texture_data);

    free(font_texture_data);

    FT_Done_Face(face);
    FT_Done_FreeType(library);

    font->initialized = 1;
    return font;
}

void bbutil_render_text(font_t* font, const char* msg, float x, float y, float r, float g, float b, float a) {
    int i, c;
    GLfloat *vertices;
    GLfloat *texture_coords;
    GLushort* indices;

    float pen_x = 0.0f;

    if (!font) {
        fprintf(stderr, "Font must not be null\n");
        return;
    }

    if (!font->initialized) {
        fprintf(stderr, "Font has not been loaded\n");
        return;
    }

    if (!msg) {
        return;
    }

    const int msg_len = strlen(msg);

    vertices = (GLfloat*) malloc(sizeof(GLfloat) * 8 * msg_len);
    texture_coords = (GLfloat*) malloc(sizeof(GLfloat) * 8 * msg_len);

    indices = (GLushort*) malloc(sizeof(GLushort) * 6 * msg_len);

    for(i = 0; i < msg_len; ++i) {
        c = msg[i];

        vertices[8 * i + 0] = x + pen_x + font->offset_x[c];
        vertices[8 * i + 1] = y + font->offset_y[c];
        vertices[8 * i + 2] = vertices[8 * i + 0] + font->width[c];
        vertices[8 * i + 3] = vertices[8 * i + 1];
        vertices[8 * i + 4] = vertices[8 * i + 0];
        vertices[8 * i + 5] = vertices[8 * i + 1] + font->height[c];
        vertices[8 * i + 6] = vertices[8 * i + 2];
        vertices[8 * i + 7] = vertices[8 * i + 5];

        texture_coords[8 * i + 0] = font->tex_x1[c];
        texture_coords[8 * i + 1] = font->tex_y2[c];
        texture_coords[8 * i + 2] = font->tex_x2[c];
        texture_coords[8 * i + 3] = font->tex_y2[c];
        texture_coords[8 * i + 4] = font->tex_x1[c];
        texture_coords[8 * i + 5] = font->tex_y1[c];
        texture_coords[8 * i + 6] = font->tex_x2[c];
        texture_coords[8 * i + 7] = font->tex_y1[c];

        indices[i * 6 + 0] = 4 * i + 0;
        indices[i * 6 + 1] = 4 * i + 1;
        indices[i * 6 + 2] = 4 * i + 2;
        indices[i * 6 + 3] = 4 * i + 2;
        indices[i * 6 + 4] = 4 * i + 1;
        indices[i * 6 + 5] = 4 * i + 3;

        //Assume we are only working with typewriter fonts
        pen_x += font->advance[c];
    }
#ifdef USING_GL11
    glEnable(GL_TEXTURE_2D);
    glEnable(GL_BLEND);

    glBlendFunc(GL_ONE, GL_ONE_MINUS_SRC_ALPHA);

    glEnableClientState(GL_VERTEX_ARRAY);
    glEnableClientState(GL_TEXTURE_COORD_ARRAY);

    glColor4f(r, g, b, a);

    glVertexPointer(2, GL_FLOAT, 0, vertices);
    glTexCoordPointer(2, GL_FLOAT, 0, texture_coords);
    glBindTexture(GL_TEXTURE_2D, font->font_texture);

    glDrawElements(GL_TRIANGLES, 6 * msg_len, GL_UNSIGNED_SHORT, indices);

    glDisableClientState(GL_TEXTURE_COORD_ARRAY);
    glDisableClientState(GL_VERTEX_ARRAY);
    glDisable(GL_TEXTURE_2D);
    glDisable(GL_BLEND);
#elif defined USING_GL20
    if (!text_program_initialized) {
        GLint status;

        // Create shaders if this hasn't been done already
        const char* v_source =
                "precision mediump float;"
                "attribute vec2 a_position;"
                "attribute vec2 a_texcoord;"
                "varying vec2 v_texcoord;"
                "void main()"
                "{"
                "   gl_Position = vec4(a_position, 0.0, 1.0);"
                "    v_texcoord = a_texcoord;"
                "}";

        const char* f_source =
                "precision lowp float;"
                "varying vec2 v_texcoord;"
                "uniform sampler2D u_font_texture;"
                "uniform vec4 u_col;"
                "void main()"
                "{"
                "    vec4 temp = texture2D(u_font_texture, v_texcoord);"
                "    gl_FragColor = u_col * temp;"
                "}";

        // Compile the vertex shader
        GLuint vs = glCreateShader(GL_VERTEX_SHADER);

        if (!vs) {
            fprintf(stderr, "Failed to create vertex shader: %d\n", glGetError());
            return;
        } else {
            glShaderSource(vs, 1, &v_source, 0);
            glCompileShader(vs);
            glGetShaderiv(vs, GL_COMPILE_STATUS, &status);
            if (GL_FALSE == status) {
                GLchar log[256];
                glGetShaderInfoLog(vs, 256, NULL, log);

                fprintf(stderr, "Failed to compile vertex shader: %s\n", log);

                glDeleteShader(vs);
            }
        }

        // Compile the fragment shader
        GLuint fs = glCreateShader(GL_FRAGMENT_SHADER);

        if (!fs) {
            fprintf(stderr, "Failed to create fragment shader: %d\n", glGetError());
            return;
        } else {
            glShaderSource(fs, 1, &f_source, 0);
            glCompileShader(fs);
            glGetShaderiv(fs, GL_COMPILE_STATUS, &status);
            if (GL_FALSE == status) {
                GLchar log[256];
                glGetShaderInfoLog(fs, 256, NULL, log);

                fprintf(stderr, "Failed to compile fragment shader: %s\n", log);

                glDeleteShader(vs);
                glDeleteShader(fs);

                return;
            }
        }

        // Create and link the program
        text_rendering_program = glCreateProgram();
        if (text_rendering_program)
        {
            glAttachShader(text_rendering_program, vs);
            glAttachShader(text_rendering_program, fs);
            glLinkProgram(text_rendering_program);

            glGetProgramiv(text_rendering_program, GL_LINK_STATUS, &status);
            if (status == GL_FALSE)    {
                GLchar log[256];
                glGetProgramInfoLog(fs, 256, NULL, log);

                fprintf(stderr, "Failed to link text rendering shader program: %s\n", log);

                glDeleteProgram(text_rendering_program);
                text_rendering_program = 0;

                return;
            }
        } else {
            fprintf(stderr, "Failed to create a shader program\n");

            glDeleteShader(vs);
            glDeleteShader(fs);
            return;
        }

        // We don't need the shaders anymore - the program is enough
        glDeleteShader(fs);
        glDeleteShader(vs);

        glUseProgram(text_rendering_program);

        // Store the locations of the shader variables we need later
        positionLoc = glGetAttribLocation(text_rendering_program, "a_position");
        texcoordLoc = glGetAttribLocation(text_rendering_program, "a_texcoord");
        textureLoc = glGetUniformLocation(text_rendering_program, "u_font_texture");
        colorLoc = glGetUniformLocation(text_rendering_program, "u_col");

        text_program_initialized = 1;
    }

    glEnable(GL_BLEND);

    //Map text coordinates from (0...surface width, 0...surface height) to (-1...1, -1...1)
    //this make our vertex shader very simple and also works irrespective of orientation changes
    EGLint surface_width, surface_height;

    eglQuerySurface(egl_disp, egl_surf, EGL_WIDTH, &surface_width);
    eglQuerySurface(egl_disp, egl_surf, EGL_HEIGHT, &surface_height);

    for(i = 0; i < 4 * msg_len; ++i) {
        vertices[2 * i + 0] = 2 * vertices[2 * i + 0] / surface_width - 1.0f;
        vertices[2 * i + 1] = 2 * vertices[2 * i + 1] / surface_height - 1.0f;
    }

    //Render text
    glUseProgram(text_rendering_program);

    glBlendFunc(GL_ONE, GL_ONE_MINUS_SRC_ALPHA);

    glBindBuffer(GL_ARRAY_BUFFER, 0);

    glActiveTexture(GL_TEXTURE0);
    glBindTexture(GL_TEXTURE_2D, font->font_texture);
    glUniform1i(textureLoc, 0);

    glUniform4f(colorLoc, r, g, b, a);

    glEnableVertexAttribArray(positionLoc);
    glVertexAttribPointer(positionLoc, 2, GL_FLOAT, GL_FALSE, 0, vertices);

    glEnableVertexAttribArray(texcoordLoc);
    glVertexAttribPointer(texcoordLoc, 2, GL_FLOAT, GL_FALSE, 0, texture_coords);

       //Draw the string
    glDrawElements(GL_TRIANGLES, 6 * msg_len, GL_UNSIGNED_SHORT, indices);

    glDisableVertexAttribArray(positionLoc);
    glDisableVertexAttribArray(texcoordLoc);
#else
    fprintf(stderr, "bbutil should be compiled with either USING_GL11 or USING_GL20 -D flags\n");
#endif

    free(vertices);
    free(texture_coords);
    free(indices);
}

void bbutil_destroy_font(font_t* font) {
    if (!font) {
        return;
    }

    glDeleteTextures(1, &(font->font_texture));

    free(font);
}

void bbutil_measure_text(font_t* font, const char* msg, float* width, float* height) {
    int i, c;

    if (!msg) {
        return;
    }

    const int msg_len  =strlen(msg);

    if (width) {
        //Width of a text rectangle is a sum advances for every glyph in a string
        *width = 0.0f;

        for(i = 0; i < msg_len; ++i) {
            c = msg[i];
            *width += font->advance[c];
        }
    }

    if (height) {
        //Height of a text rectangle is a high of a tallest glyph in a string
        *height = 0.0f;

        for(i = 0; i < msg_len; ++i) {
            c = msg[i];

            if (*height < font->height[c]) {
                *height = font->height[c];
            }
        }
    }
}

int bbutil_load_texture(const char* filename, int* width, int* height, float* tex_x, float* tex_y, unsigned int *tex) {
    int i;
    GLuint format;
    //header for testing if it is a png
    png_byte header[8];

    if (!tex) {
        return EXIT_FAILURE;
    }

    //open file as binary
    FILE *fp = fopen(filename, "rb");
    if (!fp) {
        return EXIT_FAILURE;
    }

    //read the header
    fread(header, 1, 8, fp);

    //test if png
    int is_png = !png_sig_cmp(header, 0, 8);
    if (!is_png) {
        fclose(fp);
        return EXIT_FAILURE;
    }

    //create png struct
    png_structp png_ptr = png_create_read_struct(PNG_LIBPNG_VER_STRING, NULL, NULL, NULL);
    if (!png_ptr) {
        fclose(fp);
        return EXIT_FAILURE;
    }

    //create png info struct
    png_infop info_ptr = png_create_info_struct(png_ptr);
    if (!info_ptr) {
        png_destroy_read_struct(&png_ptr, (png_infopp) NULL, (png_infopp) NULL);
        fclose(fp);
        return EXIT_FAILURE;
    }

    //create png info struct
    png_infop end_info = png_create_info_struct(png_ptr);
    if (!end_info) {
        png_destroy_read_struct(&png_ptr, &info_ptr, (png_infopp) NULL);
        fclose(fp);
        return EXIT_FAILURE;
    }

    //setup error handling (required without using custom error handlers above)
    if (setjmp(png_jmpbuf(png_ptr))) {
        png_destroy_read_struct(&png_ptr, &info_ptr, &end_info);
        fclose(fp);
        return EXIT_FAILURE;
    }

    //init png reading
    png_init_io(png_ptr, fp);

    //let libpng know you already read the first 8 bytes
    png_set_sig_bytes(png_ptr, 8);

    // read all the info up to the image data
    png_read_info(png_ptr, info_ptr);

    //variables to pass to get info
    int bit_depth, color_type;
    png_uint_32 image_width, image_height;

    // get info about png
    png_get_IHDR(png_ptr, info_ptr, &image_width, &image_height, &bit_depth, &color_type, NULL, NULL, NULL);

    switch (color_type)
    {
        case PNG_COLOR_TYPE_RGBA:
            format = GL_RGBA;
            break;
        case PNG_COLOR_TYPE_RGB:
            format = GL_RGB;
            break;
        default:
            fprintf(stderr,"Unsupported PNG color type (%d) for texture: %s", (int)color_type, filename);
            fclose(fp);
            png_destroy_read_struct(&png_ptr, &info_ptr, &end_info);
            return NULL;
    }

    // Update the png info struct.
    png_read_update_info(png_ptr, info_ptr);

    // Row size in bytes.
    int rowbytes = png_get_rowbytes(png_ptr, info_ptr);

    // Allocate the image_data as a big block, to be given to opengl
    png_byte *image_data = (png_byte*) malloc(sizeof(png_byte) * rowbytes * image_height);

    if (!image_data) {
        //clean up memory and close stuff
        png_destroy_read_struct(&png_ptr, &info_ptr, &end_info);
        fclose(fp);
        return EXIT_FAILURE;
    }

    //row_pointers is for pointing to image_data for reading the png with libpng
    png_bytep *row_pointers = (png_bytep*) malloc(sizeof(png_bytep) * image_height);
    if (!row_pointers) {
        //clean up memory and close stuff
        png_destroy_read_struct(&png_ptr, &info_ptr, &end_info);
        free(image_data);
        fclose(fp);
        return EXIT_FAILURE;
    }

    // set the individual row_pointers to point at the correct offsets of image_data
    for (i = 0; i < image_height; i++) {
        row_pointers[image_height - 1 - i] = image_data + i * rowbytes;
    }

    //read the png into image_data through row_pointers
    png_read_image(png_ptr, row_pointers);

    int tex_width, tex_height;

    tex_width = nextp2(image_width);
    tex_height = nextp2(image_height);

    glGenTextures(1, tex);
    glBindTexture(GL_TEXTURE_2D, (*tex));
    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);

    glPixelStorei(GL_UNPACK_ALIGNMENT, 1);

    if ((tex_width != image_width) || (tex_height != image_height) ) {
        glTexImage2D(GL_TEXTURE_2D, 0, format, tex_width, tex_height, 0, format, GL_UNSIGNED_BYTE, NULL);
        glTexSubImage2D(GL_TEXTURE_2D, 0, 0, 0, image_width, image_height, format, GL_UNSIGNED_BYTE, image_data);
    } else {
        glTexImage2D(GL_TEXTURE_2D, 0, format, tex_width, tex_height, 0, format, GL_UNSIGNED_BYTE, image_data);
    }

    GLint err = glGetError();

    //clean up memory and close stuff
    png_destroy_read_struct(&png_ptr, &info_ptr, &end_info);
    free(image_data);
    free(row_pointers);
    fclose(fp);

    if (err == 0) {
        //Return physical with and height of texture if pointers are not null
        if(width) {
            *width = image_width;
        }
        if (height) {
            *height = image_height;
        }
        //Return modified texture coordinates if pointers are not null
        if(tex_x) {
            *tex_x = ((float) image_width - 0.5f) / ((float)tex_width);
        }
        if(tex_y) {
            *tex_y = ((float) image_height - 0.5f) / ((float)tex_height);
        }
        return EXIT_SUCCESS;
    } else {
        fprintf(stderr, "GL error %i \n", err);
        return EXIT_FAILURE;
    }
}

int bbutil_calculate_dpi(screen_context_t ctx) {
    int rc;
    int screen_phys_size[2];

    rc = screen_get_display_property_iv(screen_disp, SCREEN_PROPERTY_PHYSICAL_SIZE, screen_phys_size);
    if (rc) {
        perror("screen_get_display_property_iv");
        bbutil_terminate();
        return EXIT_FAILURE;
    }

    //Simulator will return 0,0 for physical size of the screen, so use 170 as default dpi
    if ((screen_phys_size[0] == 0) && (screen_phys_size[1] == 0)) {
        return 170;
    } else {
        int screen_resolution[2];
        rc = screen_get_display_property_iv(screen_disp, SCREEN_PROPERTY_SIZE, screen_resolution);
        if (rc) {
            perror("screen_get_display_property_iv");
            bbutil_terminate();
            return EXIT_FAILURE;
        }
        double diagonal_pixels = sqrt(screen_resolution[0] * screen_resolution[0] + screen_resolution[1] * screen_resolution[1]);
        double diagonal_inches = 0.0393700787 * sqrt(screen_phys_size[0] * screen_phys_size[0] + screen_phys_size[1] * screen_phys_size[1]);
        return (int)(diagonal_pixels / diagonal_inches + 0.5);

    }
}

int bbutil_rotate_screen_surface(int angle) {
    int rc, rotation, skip = 1, temp;;
    EGLint interval = 1;
    int size[2];

    if ((angle != 0) && (angle != 90) && (angle != 180) && (angle != 270)) {
        fprintf(stderr, "Invalid angle\n");
        return EXIT_FAILURE;
    }

    rc = screen_get_window_property_iv(screen_win, SCREEN_PROPERTY_ROTATION, &rotation);
    if (rc) {
        perror("screen_set_window_property_iv");
        return EXIT_FAILURE;
    }

    rc = screen_get_window_property_iv(screen_win, SCREEN_PROPERTY_BUFFER_SIZE, size);
    if (rc) {
        perror("screen_set_window_property_iv");
        return EXIT_FAILURE;
    }

    switch (angle - rotation) {
        case -270:
        case -90:
        case 90:
        case 270:
            temp = size[0];
            size[0] = size[1];
            size[1] = temp;
            skip = 0;
            break;
    }

    if (!skip) {
        rc = eglMakeCurrent(egl_disp, NULL, NULL, NULL);
        if (rc != EGL_TRUE) {
            bbutil_egl_perror("eglMakeCurrent");
            return EXIT_FAILURE;
        }

        rc = eglDestroySurface(egl_disp, egl_surf);
        if (rc != EGL_TRUE) {
            bbutil_egl_perror("eglMakeCurrent");
            return EXIT_FAILURE;
        }

        rc = screen_set_window_property_iv(screen_win, SCREEN_PROPERTY_SOURCE_SIZE, size);
        if (rc) {
            perror("screen_set_window_property_iv");
            return EXIT_FAILURE;
        }

        rc = screen_set_window_property_iv(screen_win, SCREEN_PROPERTY_BUFFER_SIZE, size);
        if (rc) {
            perror("screen_set_window_property_iv");
            return EXIT_FAILURE;
        }
        egl_surf = eglCreateWindowSurface(egl_disp, egl_conf, screen_win, NULL);
        if (egl_surf == EGL_NO_SURFACE) {
            bbutil_egl_perror("eglCreateWindowSurface");
            return EXIT_FAILURE;
        }

        rc = eglMakeCurrent(egl_disp, egl_surf, egl_surf, egl_ctx);
        if (rc != EGL_TRUE) {
            bbutil_egl_perror("eglMakeCurrent");
            return EXIT_FAILURE;
        }

        rc = eglSwapInterval(egl_disp, interval);
        if (rc != EGL_TRUE) {
            bbutil_egl_perror("eglSwapInterval");
            return EXIT_FAILURE;
        }
    }

    rc = screen_set_window_property_iv(screen_win, SCREEN_PROPERTY_ROTATION, &angle);
    if (rc) {
        perror("screen_set_window_property_iv");
        return EXIT_FAILURE;
    }

    return EXIT_SUCCESS;
}