OpenGL 2d纹理不起作用

Question

I'm working on a 2D game project, and I wanted to wrap the openGl texture in a simple class. The texture is read from a 128x128px .png (with alpha channel) using libpng . Since the amount of code is pretty large, I'm using pastebin.

The code files:

• Texture class: http://pastebin.com/gbGMEF2Z
• PngReader class: http://pastebin.com/h6uP5Uc8 (seems to work okay, so I removed the description).
• OpenGl code: http://pastebin.com/PVhwnDif

To avoid wasting your time, I will explain the code a little bit:

• Texture class : a wrapper for an OpenGL texture. The loadData function sets up the texture in gl (this is the function I suspect that doesn't work).

• OpenGl code : the debugSetTexture function puts a texture in the temp variable which is used in the graphicsDraw() function. This is because it is not in the same source file as main() . In the graphicsMainLoop() function, I use the Fork() function which in fact calls fork() , and stores the pid of the spawned process.

From main() , this is what I do:

Strategy::IO::PngReader reader ("/cygdrive/c/Users/Tibi/Desktop/128x128.png");
reader.read();
grahpicsInit2D(&argc, argv);
debugSetTexture(reader.generateTexture());
graphicsMainLoop();
reader.close();

I tried an application called gDEBugger, and in the texture viewer, there was a texture generated, but size was 0x0px.

I suspect that the problem happens when the texture is loaded using Texture::loadTexture().

Answer 1

You need to check GL error codes after GL calls.

For example add this method to your class:

GLuint Texture::checkError(const char *context)
{
  GLuint err = glGetError();
  if (err > 0 )  { 
    std::cout << "0x" << std::hex << err << " glGetError() in " << context 
    << std::endl;
  }
  return err;
}

then call it like so:

glBindTexture(GL_TEXTURE_2D, handle);
checkError("glBindTexture");

Assuming it succeeds in loading the png file, suppose your program fails in glBindTexture? (strong hint)

You did call your Error function for your file handling, but does your program halt then or chug on?

Here's a serious issue: Texture PngReader::generateTexture() returns Texture by value. This will cause your Texture object to be copied on return (handle and all) and then ~Texture() to be called, destroying the stack-based copy. So your program will call glDeleteTextures a couple times!

If you want to return it by value, you could wrap it in a shared_ptr<> which does reference counting. This would cause the destructor to be called only once:

#include <tr1/memory>
typedef std::tr1::shared_ptr<Texture> TexturePtr;

Use TexturePtr as your return type. Initialize it in generateTexture() like this:

TexturePtr t(new Texture);

then change all the method access to go through -> instead of .