texture.sj

texture(
    size : size()
    id : 0u

    getSize() { size(size.w, size.h) }
) {
    this
} copy {
    --c--
    glid_retain(_this->id);
    --c--
} destroy {
    --c--
    if (glid_release(_this->id)) {
        glDeleteTextures(1, &_this->id);
    }
    --c--
}

texture_fromElement(element : '#element, size : 'size) {
    scenebuffer : scenebuffer(size)

    element.setRect(rect(0, 0, size.w, size.h))

    scene : scene2d()
    scene.setSize(size)
    glPushFramebuffer(scenebuffer.framebuffer)
    scene.start()
    element.render(scene)
    scene.end()
    glPopFramebuffer(scenebuffer.framebuffer)

    scenebuffer.texture
}

texture_fromPng(fileName : 'string) {
    id := 0u
    w := 0
    h := 0
    --c--
    id = png_texture_load((char*)filename->data.data, &w, &h);
    --c--
    texture(size(w, h), id)
}

--cfunction--
#include(<png.h>)

GLuint png_texture_load(const char * file_name, int * width, int * height)
{
    // This function was originally written by David Grayson for
    // https://github.com/DavidEGrayson/ahrs-visualizer

    png_byte header[8];

    FILE *fp = fopen(file_name, "rb");
    if (fp == 0)
    {
        perror(file_name);
        return 0;
    }

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

    if (png_sig_cmp(header, 0, 8))
    {
        fprintf(stderr, "error: %s is not a PNG.\n", file_name);
        fclose(fp);
        return 0;
    }

    png_structp png_ptr = png_create_read_struct(PNG_LIBPNG_VER_STRING, NULL, NULL, NULL);
    if (!png_ptr)
    {
        fprintf(stderr, "error: png_create_read_struct returned 0.\n");
        fclose(fp);
        return 0;
    }

    // create png info struct
    png_infop info_ptr = png_create_info_struct(png_ptr);
    if (!info_ptr)
    {
        fprintf(stderr, "error: png_create_info_struct returned 0.\n");
        png_destroy_read_struct(&png_ptr, (png_infopp)NULL, (png_infopp)NULL);
        fclose(fp);
        return 0;
    }

    // create png info struct
    png_infop end_info = png_create_info_struct(png_ptr);
    if (!end_info)
    {
        fprintf(stderr, "error: png_create_info_struct returned 0.\n");
        png_destroy_read_struct(&png_ptr, &info_ptr, (png_infopp) NULL);
        fclose(fp);
        return 0;
    }

    // the code in this if statement gets called if libpng encounters an error
    if (setjmp(png_jmpbuf(png_ptr))) {
        fprintf(stderr, "error from libpng\n");
        png_destroy_read_struct(&png_ptr, &info_ptr, &end_info);
        fclose(fp);
        return 0;
    }

    // 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 temp_width, temp_height;

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

    if (width){ *width = temp_width; }
    if (height){ *height = temp_height; }

    //printf("%s: %lux%lu %d\n", file_name, temp_width, temp_height, color_type);

    if (bit_depth != 8)
    {
        fprintf(stderr, "%s: Unsupported bit depth %d.  Must be 8.\n", file_name, bit_depth);
        return 0;
    }

    GLint format;
    switch(color_type)
    {
    case PNG_COLOR_TYPE_RGB:
        format = GL_RGB;
        break;
    case PNG_COLOR_TYPE_RGB_ALPHA:
        format = GL_RGBA;
        break;
    default:
        fprintf(stderr, "%s: Unknown libpng color type %d.\n", file_name, color_type);
        return 0;
    }

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

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

    // glTexImage2d requires rows to be 4-byte aligned
    rowbytes += 3 - ((rowbytes-1) % 4);

    // Allocate the image_data as a big block, to be given to opengl
    png_byte * image_data = (png_byte *)malloc(rowbytes * temp_height * sizeof(png_byte)+15);
    if (image_data == NULL)
    {
        fprintf(stderr, "error: could not allocate memory for PNG image data\n");
        png_destroy_read_struct(&png_ptr, &info_ptr, &end_info);
        fclose(fp);
        return 0;
    }

    // row_pointers is for pointing to image_data for reading the png with libpng
    png_byte ** row_pointers = (png_byte **)malloc(temp_height * sizeof(png_byte *));
    if (row_pointers == NULL)
    {
        fprintf(stderr, "error: could not allocate memory for PNG row pointers\n");
        png_destroy_read_struct(&png_ptr, &info_ptr, &end_info);
        free(image_data);
        fclose(fp);
        return 0;
    }

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

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

    // Generate the OpenGL texture object
    GLuint texture;
    glGenTextures(1, &texture);
    glBindTexture(GL_TEXTURE_2D, texture);
    glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE );
    glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE );
    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, format, temp_width, temp_height, 0, format, GL_UNSIGNED_BYTE, image_data);

    // clean up
    png_destroy_read_struct(&png_ptr, &info_ptr, &end_info);
    free(image_data);
    free(row_pointers);
    fclose(fp);
    return texture;
}
--cfunction--