OpenGL ES2.0: What's wrong with these shaders?

Question

I'm trying to follow a FreeType2 tutorial here but I cannot get the shaders to link.

Is there something wrong with these shaders?

Vertex shader:

attribute vec4 coord;
varying vec2 texcoord;

void main()
{
  gl_Position = vec4( coord.xy, 0, 1 );
  texcoord = coord.zw;
}

Fragment shader:

varying vec2 texcoord;
uniform sampler2D tex;
uniform vec4 color;

void main()
{
  gl_FragColor = vec4(1, 1, 1, texture2D( tex, texcoord ).r ) * color;
}

I have successfully uses the below function calls with my own shaders for doing simple solid filling and simple textures. I have no idea why I can't use the above shaders.

Here's the code which compilers and links the shaders into the program:

GLuint BuildShader( char *pszSource, GLenum shaderType )
{
  GLuint hShader = glCreateShader( shaderType );
  glShaderSource(hShader, 1, &pszSource, 0 );
  glCompileShader( hShader );

  GLint compileSuccess = GL_FALSE;

  glGetShaderv( hShader, GL_COMPILE_STATUS, &compileSuccess );      

  if( compileSuccess == GL_FALSE )
  {
    GLchar message[ 256 ];
    glGetShaderInfoLog( hShader, sizeof( message ), 0, &message[ 0 ] );
    printf( "SHADER (%s) %s\n", pszSource, message );
    exit( 1 );
  }

  return hShader;
}

GLuint BuildProgram( char *pszVertexShaderSource, char *pszFragmentShaderSource )
{
  GLuint vShader = BuildShader( pszVertexShaderSource,   GL_VERTEX_SHADER );
  GLuint fShader = BuildShader( pszFragmentShaderSource, GL_FRAGMENT_SHADER );

  GLuint hProgram = glCreateProgram();
  glAttachShader( hProgram, vShader );
  glAttachShader( hProgram, fShader );
  glLinkProgram( hProgram );

  GLint linkSuccess;

  glGetProgramiv( hProgram, GL_LINK_STATUS, &linkSuccess );

  if( linkSuccess == GL_FALSE )
  {
    GLchar message[ 256 ];
    glGetProgramInfoLog( hProgram, sizeof( message ), 0, &message[ 0 ] );
    printf( "BUILD %s\n", message );
    exit( 1 );
  }

  return hProgram;
}

...
g_FontProgram = BuildProgram( vsFont, fsFont );
...

I get the below output at the linking phase:

BUILD ERROR: One or more attached shaders not successfully compiled

UPDATE: I have fixed the shader compilation check. Now I get the following error:

SHADER (varying vec2 texcoord; uniform sampler2D tex; uniform vec4 color; void main() { gl_FragColor = vec4(1, 1, 1, texture2D( tex, texcoord ).r ) * color; }) ERROR: 0:1: 'vec2' : declaration must include a precision qualifier for type
ERROR: 0:1: 'vec4' : declaration must include a precision qualifier for type
ERROR: 0:1: Use of undeclared identifier 'texcoord'
ERROR: 0:1: Use of undeclared identifier 'color'

It might not be the issue here, but always double's instead of ints, ie "0.0" and "1.0" instead of "0" and "1". Some GPU's are picky about that. — reden, Apr 12 '16 at 09:53
The error looks to be self explanatory. At the moment of linking you are linking 2 objects, one of which failed to compile. Why don't you debug and error check the function "BuildShader"? — Maurizio Benedetti, Apr 12 '16 at 13:04
`GLint compileSuccess;` You forgot to initialize this variable. — Nicol Bolas, Apr 12 '16 at 15:22
@Nicol Bolas: Thank you. Must have been too tired to see the obvious. I updated my question with what was needed. Once I had the shader error, it was obvious. — SparkyNZ, Apr 12 '16 at 19:08
@NicolBolas: I don't understand why this question is [On Hold]. The tutorial I was following was intended for OpenGL. It has a fragment shader that doesn't work with OpenGL ES2, and I have answered my own question with the reason why. Surely somebody else will attempt the same tutorial and may be stuck because of the same reason? — SparkyNZ, Apr 14 '16 at 00:08
@SparkyNZ: Whether it's from a tutorial or not, it's still just a typo. — Nicol Bolas, Apr 14 '16 at 01:24
@NicolBolas: You mean the tutorial itself is wrong and "precision mediump float" should have been included regardless of whether it was OpenGL or OpenGL ES? — SparkyNZ, Apr 14 '16 at 01:27
@SparkyNZ: If it's an OpenGL ES tutorial, yes. If it's a desktop GL tutorial, no. But in either case, *you* not putting it in *your code* (whether you copy-and-pasted it or not) is still functionally a typo. — Nicol Bolas, Apr 14 '16 at 01:29
@NicolBolas: OK. Lets just delete the question then. I got what I needed in the end with your help. — SparkyNZ, Apr 14 '16 at 01:34

SparkyNZ · Accepted Answer · 2016-04-14T00:10:10.917

0

The shaders failed to compile because the following line was needed:

precision mediump float;

For anyone else trying to follow the same tutorial, the following fragment shader will work under OpenGL ES2.0:

precision mediump float;
varying vec2 texcoord;
uniform sampler2D tex;
uniform vec4 color;

void main()
{
  gl_FragColor = vec4(1, 1, 1, texture2D( tex, texcoord ).r ) * color;
}

edited Apr 14 '16 at 00:10

answered Apr 12 '16 at 19:07

SparkyNZ

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OpenGL ES2.0: What's wrong with these shaders?

1 Answers1