Question

I am working on an application using OpenGL ES 2.0 for an embedded device.

This is my fragment shader:

varying vec2 v_texCoord;
uniform sampler2D s_texture;
void main() {
  gl_FragColor = texture2D(s_texture, v_texCoord);
}

I set up the textures properly. For some reason, calling glTexImage2D is not producing the result I’m looking for. The texture is entirely black, rather than being filled with the data I provide it.

This is how I create the texture:

   GLuint textureId;

   // 2x2 Image, 3 bytes per pixel (R, G, B)
   GLubyte pixels[6 * 3] =
   {  
      255,   0,   0, // Red
        0, 255,   0, // Green
        0,   0, 255, // Blue
      255, 255,   0,  // Yellow
        0, 255, 255,
        255, 0, 255
   };

   // Use tightly packed data
   glPixelStorei ( GL_UNPACK_ALIGNMENT, 1 );

   // Generate a texture object
   glGenTextures ( 1, &textureId );

   // Bind the texture object
   glBindTexture ( GL_TEXTURE_2D, textureId );

   // Load the texture
   glTexImage2D ( GL_TEXTURE_2D, 0, GL_RGB, 3, 2, 0, GL_RGB, GL_UNSIGNED_BYTE, pixels );


   // Set the filtering mode
   glTexParameteri ( GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST );
   glTexParameteri ( GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST );

Afterward, I bind the texture like so:

samplerLoc = glGetUniformLocation ( userData->programObject, "s_texture" );
glActiveTexture ( GL_TEXTURE0 );
glBindTexture ( GL_TEXTURE_2D, textureId );

// Set the sampler texture unit to 0
glUniform1i ( samplerLoc, 0 );

I confirmed that the vertex and texture coordinates are bound and passed to the shaders when debugging. So, it has to be an issue with s_texture or the glTexImage2D function itself.

Answer 1

You need to set the clamp modes to CLAMP_TO_EDGE for both U and V dimensions, otherwise the texture is incomplete and will sample as black.