Font Texture Alignment Issue

Graphics and GPU Programming Programming OpenGL

Started by Zorbfish April 27, 2009 12:42 PM

0 comments, last by Sik_the_hedgehog 14 years, 12 months ago

214

Author

April 27, 2009 12:42 PM

I've been working on font rendering in OpenGL and have run into a big of a snag. When copying the bitmap generated by the FreeType library into an OpenGL texture the bitmap is not rendered correctly. After many hours of debugging/traces I believe it is related to the format of the texture and possibly that I am not providing the data in the correct alignment; but I am unsure (I have not worked with OpenGL for a LONG time). I'm hoping a few more eyes here can help me pick up on my mistake. Thanks. Here's the example code I was working with:

#include <SDL.h>
#include <windows.h>
#include <GL\GL.h>
#include "ft2build.h"
#include <freetype/freetype.h>
#include <freetype/ftglyph.h>
#include <freetype/ftoutln.h>
#include <freetype/fttrigon.h>
#include FT_FREETYPE_H
#include <stdio.h>

typedef struct {
  int width;
  int height;
  int xoffset;
  int yoffset;
  float texels[4];
} Glyph;

int SDL_main(int argc, char *argA[]) {
  SDL_Event event = {0};
  int running = 1;
  GLuint texture = 0;
  GLubyte *empty_data = 0;
  int x = 50;
  int y = 50;
  int i, j;
  int ok = 0;
  const GLsizei TEXTURE_SIZE = 128;

  FT_Library lib;
  FT_Face face;
  FT_Bitmap *bitmap;
  FT_Glyph glyph;
  FT_BitmapGlyph bitmap_glyph;
  GLubyte* padded_bitmap;
  int bw = 0;
  int bh = 0;
  int texNext = 0;
  FT_UInt b_glyph = 0;
  FT_UInt A_glyph = 0;
  Glyph b, A;
  FT_Vector kerning = {0};
  FILE *test;

  ok = !FT_Init_FreeType(&lib);
  if (ok) {
    FT_New_Face(lib, "Verdana.ttf", 0, &face);
    FT_Set_Char_Size(face, 16*64, 16*64, 96, 96);
  }

  SDL_Init(SDL_INIT_VIDEO);
  SDL_GL_SetAttribute(SDL_GL_RED_SIZE, 8);
  SDL_GL_SetAttribute(SDL_GL_GREEN_SIZE, 8);
  SDL_GL_SetAttribute(SDL_GL_BLUE_SIZE, 8);
  SDL_GL_SetAttribute(SDL_GL_ALPHA_SIZE, 8);
  SDL_SetVideoMode(800, 600, 24, SDL_OPENGL);

  glEnable(GL_BLEND);
  glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);

  glEnable(GL_TEXTURE_2D);
  glGenTextures(1, &texture);
  glBindTexture(GL_TEXTURE_2D, texture);
  glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
  glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
  glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP);
  glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP);

  empty_data = calloc(2 * TEXTURE_SIZE * TEXTURE_SIZE, sizeof(GLubyte));
  glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, TEXTURE_SIZE, TEXTURE_SIZE, 0, GL_LUMINANCE_ALPHA, GL_UNSIGNED_BYTE, empty_data);
  free(empty_data);

  test = fopen("out.txt", "w");

  b_glyph = FT_Get_Char_Index(face, 'b');
  FT_Load_Char(face, 'b', FT_LOAD_DEFAULT);
  FT_Get_Glyph(face->glyph, &glyph);
  if ( glyph->format != FT_GLYPH_FORMAT_BITMAP ) {
    FT_Glyph_To_Bitmap(&glyph, FT_RENDER_MODE_NORMAL, 0, 1);
  }
  bitmap_glyph = (FT_BitmapGlyph)glyph;
  bitmap = &bitmap_glyph->bitmap;
  bw = bitmap->width;
  bh = bitmap->rows;

  /* pad to add alpha */
  padded_bitmap = calloc(2 * bw * bh, sizeof(GLubyte));
  memset(padded_bitmap, 0, 2*bw*bh*sizeof(GLubyte));
  for(j = 0; j < bh; j++) {
    for(i = 0; i < bw; i++) {
      padded_bitmap[2 * (i + j * bw)] = 255;
      padded_bitmap[2 * (i + j * bw) + 1] = bitmap->buffer[(i + j * bw)];
      putc(bitmap->buffer[(i + j * bw)] > 128 ? ' ' : '.', test);
    }
    putc('\n', test);
  }
  putc('\n', test);

  b.width = bw; b.height = bh;
  b.texels[0] = 0.0;
  b.texels[1] = 0.0;
  b.xoffset = face->glyph->bitmap_left;
  b.yoffset = face->glyph->bitmap_top;
  b.texels[2] = b.texels[0] + b.width / (float)TEXTURE_SIZE;
  b.texels[3] = b.texels[1] + b.height / (float)TEXTURE_SIZE;

  texNext += bw;

  glTexSubImage2D(GL_TEXTURE_2D, 0, 0, 0, bitmap->width, bitmap->rows, GL_LUMINANCE_ALPHA, GL_UNSIGNED_BYTE, padded_bitmap);

  free(padded_bitmap);

  A_glyph = FT_Get_Char_Index(face, 'A');

  FT_Load_Char(face, 'A', FT_LOAD_DEFAULT);
  FT_Get_Glyph(face->glyph, &glyph);
  if ( glyph->format != FT_GLYPH_FORMAT_BITMAP ) {
    FT_Glyph_To_Bitmap(&glyph, FT_RENDER_MODE_NORMAL, 0, 1);
  }
  bitmap_glyph = (FT_BitmapGlyph)glyph;
  bitmap = &bitmap_glyph->bitmap;
  bw = bitmap->width;
  bh = bitmap->rows;
  padded_bitmap = calloc(2 * bw * bh, sizeof(GLubyte));

  for(j = 0; j < bh; j++) {
    for(i = 0; i < bw; i++) {
      padded_bitmap[2 * (i + j * bw)] = 255;
      padded_bitmap[2 * (i + j * bw) + 1] = bitmap->buffer;
      putc(bitmap-&gt;buffer[(i + j * bw)] &gt; <span class="cpp-number">128</span> ? ' ' : '.', test);
    }
    putc('\n', test);
  }
  putc('\n', test);

  <span class="cpp-keyword">for</span>(j = <span class="cpp-number">0</span>; j &lt; bh; j++) {
    <span class="cpp-keyword">for</span>(i = <span class="cpp-number">0</span>; i &lt; bw; i++) {
      padded_bitmap[<span class="cpp-number">2</span> * (i + j * bw)] = <span class="cpp-number">255</span>;
      padded_bitmap[<span class="cpp-number">2</span> * (i + j * bw) + <span class="cpp-number">1</span>] = bitmap-&gt;buffer;
      putc(padded_bitmap[<span class="cpp-number">2</span> * (i + j * bw) + <span class="cpp-number">1</span>] &gt; <span class="cpp-number">128</span> ? ' ' : '.', test);
    }
    putc('\n', test);
  }
  fclose(test);

  A.width = bw; A.height = bh;
  A.xoffset = face-&gt;glyph-&gt;bitmap_left;
  A.yoffset = face-&gt;glyph-&gt;bitmap_top;
  A.texels[<span class="cpp-number">0</span>] = (<span class="cpp-keyword">float</span>)texNext / (<span class="cpp-keyword">float</span>)TEXTURE_SIZE;
  A.texels[<span class="cpp-number">1</span>] = (<span class="cpp-keyword">float</span>)<span class="cpp-number">0</span> / (<span class="cpp-keyword">float</span>)TEXTURE_SIZE;
  A.texels[<span class="cpp-number">2</span>] = A.texels[<span class="cpp-number">0</span>] + A.width / (<span class="cpp-keyword">float</span>)TEXTURE_SIZE;
  A.texels[<span class="cpp-number">3</span>] = A.texels[<span class="cpp-number">1</span>] + A.height / (<span class="cpp-keyword">float</span>)TEXTURE_SIZE;

  glTexSubImage2D(GL_TEXTURE_2D, <span class="cpp-number">0</span>, texNext, <span class="cpp-number">0</span>, bitmap-&gt;width, bitmap-&gt;rows, GL_LUMINANCE_ALPHA, GL_UNSIGNED_BYTE, padded_bitmap);
  free(padded_bitmap);

  glMatrixMode(GL_PROJECTION);
  glOrtho(<span class="cpp-number">0</span>, <span class="cpp-number">800</span>, <span class="cpp-number">600</span>, <span class="cpp-number">0</span>, -<span class="cpp-number">1</span>, <span class="cpp-number">1</span>);
  glMatrixMode(GL_MODELVIEW);
  glTranslated(<span class="cpp-number">0</span>.<span class="cpp-number">00735</span>, <span class="cpp-number">0</span>.<span class="cpp-number">00735</span>, <span class="cpp-number">0</span>.<span class="cpp-number">0</span>);

  <span class="cpp-keyword">while</span> (running) {
    glClearColor(<span class="cpp-number">0</span>, <span class="cpp-number">0</span>, <span class="cpp-number">1</span>, <span class="cpp-number">0</span>);
    glClear(GL_COLOR_BUFFER_BIT);

    SDL_WaitEvent(&amp;event);
    <span class="cpp-keyword">switch</span> (event.type) {
      <span class="cpp-keyword">case</span> SDL_KEYDOWN:
        <span class="cpp-keyword">if</span> (event.key.keysym.sym == SDLK_ESCAPE) {
          running = <span class="cpp-number">0</span>;
          <span class="cpp-keyword">break</span>;
        }
      <span class="cpp-keyword">case</span> SDL_QUIT:
        running = <span class="cpp-number">0</span>;
        <span class="cpp-keyword">break</span>;
      <span class="cpp-keyword">default</span>:
        ;
    }
    FT_Get_Kerning(face, A_glyph, b_glyph, FT_KERNING_DEFAULT, &amp;kerning);

    glBegin(GL_QUADS);

    <span class="cpp-comment">/*b*/</span>
    glTexCoord2d(b.texels[<span class="cpp-number">0</span>], b.texels[<span class="cpp-number">1</span>]); glVertex2i(x, y-b.yoffset);
    glTexCoord2d(b.texels[<span class="cpp-number">0</span>], b.texels[<span class="cpp-number">3</span>]); glVertex2i(x, y+b.height-b.yoffset);
    glTexCoord2d(b.texels[<span class="cpp-number">2</span>], b.texels[<span class="cpp-number">3</span>]); glVertex2i(x+b.width, y+b.height-b.yoffset);
    glTexCoord2d(b.texels[<span class="cpp-number">2</span>], b.texels[<span class="cpp-number">1</span>]); glVertex2i(x+b.width, y-b.yoffset);

      <span class="cpp-comment">/*A*/</span>
    glTexCoord2d(A.texels[<span class="cpp-number">0</span>], A.texels[<span class="cpp-number">1</span>]); glVertex2i(texNext+(kerning.x&gt;&gt;<span class="cpp-number">6</span>)+x, y-A.yoffset);
    glTexCoord2d(A.texels[<span class="cpp-number">0</span>], A.texels[<span class="cpp-number">3</span>]); glVertex2i(texNext+(kerning.x&gt;&gt;<span class="cpp-number">6</span>)+x, y+A.height-A.yoffset);
    glTexCoord2d(A.texels[<span class="cpp-number">2</span>], A.texels[<span class="cpp-number">3</span>]); glVertex2i(texNext+(kerning.x&gt;&gt;<span class="cpp-number">6</span>)+x+A.width, y+A.height-A.yoffset);
    glTexCoord2d(A.texels[<span class="cpp-number">2</span>], A.texels[<span class="cpp-number">1</span>]); glVertex2i(texNext+(kerning.x&gt;&gt;<span class="cpp-number">6</span>)+x+A.width, y-A.yoffset);
    glEnd();
    SDL_GL_SwapBuffers();
  }

  glDeleteTextures(<span class="cpp-number">1</span>, &amp;texture);

  <span class="cpp-keyword">if</span> (ok) {
    FT_Done_Face(face);
    FT_Done_FreeType(lib);
  }

  SDL_Quit();
  <span class="cpp-keyword">return</span> <span class="cpp-number">0</span>;
}


</pre></div><!–ENDSCRIPT–>

And here's an ASCII rep of the output. Notice that the Freetype bitmaps are rendering correctly (also I have no idea why 'b' is so messed up):
<pre>
Freetype's returned bitmaps:
  ………
  ………
  ………
  ………
  ..    …
         ..
   ….  ..
  ……  .
  ……  .
  ……  .
  ……  .
  ……  .
  ……  .
  …..  ..
        …
       ….

……   ……
…..    ……
…..     …..
…..  .  …..
….  ..  …..
….  ..   ….
….  …  ….
…  ….  ….
…  ….   …
…  …..  …
..          …
..           ..
..  …….  ..
.  ……..  ..
.  ………  .
   ………  .

What ends up &#111;n the screen:
  ………  …
……  ……..
.  ………  ..
    …         
..   ….  ..  .
…..  .  ……
  .  ……  .  
……  .  …..
.  .  ……  . 
 …..  ..      
  …       ….
.  . … … …
 ……………
  …… . …..
…….. . . . .
…. …….. ..

……   …….
….    ……..
…     ……..
..  .  ………
  ..  ……… 
 ..   ……..  
…  …….  ..
..  …….  …
.   ……  ….
.  …..        
  …..         
  ….  ……. 
 …  ……..  
…  ………  
.   ………  .
…………    
</pre>

Sik_the_hedgehog

3,003

April 27, 2009 01:10 PM

That looks like the stride has the wrong value. And that only judging from the output, not even paid attention at the code =P Check if you're setting the proper stride value for the texture data.

Don't pay much attention to "the hedgehog" in my nick, it's just because "Sik" was already taken =/ By the way, Sik is pronounced like seek, not like sick.

Font Texture Alignment Issue

This topic is closed to new replies.

Popular Topics

Recommended Tutorials

Font Texture Alignment Issue

This topic is closed to new replies.

Popular Topics

Recommended Tutorials

Reticulating splines