ufukomer / opengles-training

Introduction to OpenGL ES in Android.

OpenGL ES Training (Android)

Shaders

The steps in working with a shader object:

1. Create shader object:

   glCreateShader(int type)

   type: The type of shader to create, either GL_VERTEX_SHADER or GL_FRAGMENT_SHADER.

2. Provide shader source code:

   glShaderSource(int shader, String shaderSrc)

   shader: The shader created with glCreateShader().

   shaderSrc: Shader source code.

3. Compile the shader:

   glCompileShader(int shader)

   shader: The shader object which already has a source code.

4. Get information about compiling after compile:

   glGetShaderiv(int shader, int pname, int[] params)

   shader: The shader object to get information about.

   pname: Information parameter;

   • GL_COMPILE_STATUS
   • GL_DELETE_STATUS
   • GL_INFO_LOG_LENGTH
   • GL_SHADER_SOURCE_LENGTH
   • GL_SHADER_TYPE

   params: Integer storage location for the result of the query.

5. Get shader info log to see if error occurs and find out why:

   glGetShaderInfoLog(int shader)

   shader: The shader object which you want to get log info about.

Programs

1. Create program object:

   glCreateProgram()

2. Attach shader object to our program object created before:

   glAttachShader(int program, int shader)

   program: The program object which shader will be attached to it.

   shader: The shader object which will be attached to the program object created before with glCreateProgram() method.

3. After shaders have been attached, it is ready to link shader objects together.

   glLinkProgram(int program)

   program: The program object which shader objects attached to it with glAttachShader().

4. Check the link succeeded or not:

   glGetProgramiv (int program, int pname, int[] params, int offset)

   program: The program object to get information about.

   pname: Information parameter;

   • GL_ACTIVE_ATTRIBUTES
   • GL_ACTIVE_ATTRIBUTE_MAX_LENGTH
   • GL_ACTIVE_UNIFORM_BLOCK
   • GL_ACTIVE_UNIFORM_BLOCK_MAX_LENGTH
   • GL_ACTIVE_UNIFORMS
   • GL_ACTIVE_UNIFORM_MAX_LENGTH
   • GL_ATTACHED_SHADERS
   • GL_DELETE_STATUS
   • GL_INFO_LOG_LENGTH
   • GL_LINK_STATUS
   • GL_PROGRAM_BINARY_RETRIEVABLE_HINT
   • GL_TRANSFORM_FEEDBACK_BUFFER_MODE
   • GL_TRANSFORM_FEEDBACK_VARYINGS
   • GL_TRANSFORM_FEEDBACK_VARYING_MAX_LENGTH
   • GL_VALIDATE_STATUS

   params: Integer storage location for the result of the query.

5. Get program info log to see if error occurs and find out why:

   glGetProgramInfoLog(int program)

   program: The program object which you want to get log info about.

6. Activate the program object:

   glUseProgram(int program)

   program: The program object which will be activated for render process.