From data to OpenGL 2D Texture

Question

I am using an OpenGL 3.3 context, and GLFW3 for windowing. I am also using C. I am using STB_truetype to rasterize characters to an dynamically allocated unsigned char.

I get the data from STB_truetype as such :

unsigned char ttf_buffer[1<<25];
stbtt_fontinfo font;

fread(ttf_buffer, 1, 1<<25, fopen("Script Thing.ttf", "rb"));

stbtt_InitFont(&font, ttf_buffer, stbtt_GetFontOffsetForIndex(ttf_buffer,0));

int w,h, xoff, yoff;
int c = 'C', s = 60;

unsigned char *bitmap = stbtt_GetCodepointBitmap(&font, 0,stbtt_ScaleForPixelHeight(&font, s), c, &w, &h, &xoff,&yoff);

To make sure I have the right data, I print it to the console :

for(int i = 0; i < h; i++)
{
    for(int x = 0; x < w; x++)
    {
        printf("%c", bitmap[x+i*w]>>5 ? '1' : ' ');
    }
    printf("\n");
}

Then I create the 2D OpenGL Texture :

glGenTextures(1,&Texture);
glBindTexture(GL_TEXTURE_2D, Texture);
glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST );
glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST );
                    glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE );
                    glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE );
glTexImage2D( GL_TEXTURE_2D, 0, GL_RED, w,h,
            0, GL_RED, GL_UNSIGNED_BYTE, NewTemp );

I tested it with the 'A' character and I get :

                 11111      
                1111111     
               111111111    
              1111111111    
              11111111111   
             111111 11111   
            111111  11111   
            111111   1111   
           111111    1111   
           11111     1111   
          111111     1111   
     111111111111   11111   
   1111111111111111111111   
   111111111111111111111    
   111111111111111111111    
   111111111   1111111111   
       11111        111111  
       1111        11111111 
      11111        11111111 
      1111         11111111 
     1111          111  111 
     1111          111  1111
    1111          1111   111
    111           1111  111 
   111            111   111 
  1111            111  1111 
 1111             11111111  
1111              1111111   
 1                 111      

I render the texture OpenGL context :

It is right as you can see.

However when I try the C character :

              11       
          1111111111   
        1111111111111  
       111111111111111 
      11111111111111111
     1111111     111111
    111111        11111
   111111         1111 
   11111          1111 
  11111            11  
  1111                 
 11111                 
 1111                  
 1111                  
1111                   
1111                   
1111                   
1111                   
1111                   
111                    
111                    
1111                   
1111                   
 111                   
 1111                  
  1111              11 
  111111        11111  
   11111111111111111   
     111111111111      
          11   

Same for other characters such as 'X' :

        1111         1111 
        11111        11111
        11111       111111
        111111     111111 
         11111    1111111 
         11111   1111111  
         11111  1111111   
          1111 1111111    
          11111111111     
          1111111111      
          11111111        
          1111111         
          111111          
         111111           
        1111111           
       11111111           
      111111111           
     11111  1111          
    11111   1111          
   11111    1111          
   1111      1111         
  1111       1111         
 1111         111         
 111          1111        
111            111        
111            1111       
11              11111     
1111             11111    
 11                 1     

Any idea what I might be doing wrong? Thanks.

EDIT : Fixed it with adding glPixelStorei( GL_UNPACK_ALIGNMENT, 1); just before glTexImage2D. Thanks again to doron

Answer 1

Normally each row will be a multiple the width and the bytes per pixel. But some 2D rasterization software will require additional dead space afterwards (for alignment purposes). The jump from row to row is known as the stride and can be greater than the width. From the images you have displayed, it looks like the stride of your bitmap is greater than the width.

So what you will have to do is find out what the stride is, and either copy the bitmap into a bitmap where the stride is equal to the width or use glPixelStorei with the correct GL_UNPACK_ROW_LENGTH.