Shader.java

import static android.opengl.GLES20.GL_COMPILE_STATUS;
import static android.opengl.GLES20.GL_FRAGMENT_SHADER;
import static android.opengl.GLES20.GL_LINK_STATUS;
import static android.opengl.GLES20.GL_VALIDATE_STATUS;
import static android.opengl.GLES20.GL_VERTEX_SHADER;
import static android.opengl.GLES20.glAttachShader;
import static android.opengl.GLES20.glCompileShader;
import static android.opengl.GLES20.glCreateProgram;
import static android.opengl.GLES20.glCreateShader;
import static android.opengl.GLES20.glDeleteProgram;
import static android.opengl.GLES20.glDeleteShader;
import static android.opengl.GLES20.glGetProgramiv;
import static android.opengl.GLES20.glGetShaderiv;
import static android.opengl.GLES20.glLinkProgram;
import static android.opengl.GLES20.glShaderSource;
import static android.opengl.GLES20.glValidateProgram;

public class Shader {
  
    public static int compileShader(int type, String code) {

        final int shaderObjectId = glCreateShader(type);

        if (shaderObjectId == 0) {
            // Could not create a new shader
            return 0;
        }

        // Pass shader source
        glShaderSource(shaderObjectId, code);

        // Compile code
        glCompileShader(shaderObjectId);

        // Check Compile status, store it in first element in compileStatus array
        final int[] compileStatus = new int[1];
        glGetShaderiv(shaderObjectId, GL_COMPILE_STATUS, compileStatus, 0);

        if (compileStatus[0] == 0) {
            // If it failed, delete the shader object
            glDeleteShader(shaderObjectId);
            return 0;
        }

        return shaderObjectId;
    }

    public static boolean validateProgram(int projectObjectID) {
        glValidateProgram(projectObjectID);

        final int[] validateStatus = new int[1];
        glGetProgramiv(projectObjectID, GL_VALIDATE_STATUS, validateStatus, 0);

        return validateStatus[0] != 0;
    }

    public static int linkProgram(int vertexShaderID, int fragmentShaderID) {
        final int programObjectID = glCreateProgram();

        if (programObjectID == 0) {
            // Could not create program for shader
            return 0;
        }

        glAttachShader(programObjectID, vertexShaderID);
        glAttachShader(programObjectID, fragmentShaderID);

        glLinkProgram(programObjectID);

        final int[] linkStatus = new int[1];
        glGetProgramiv(programObjectID, GL_LINK_STATUS, linkStatus, 0);

        if (linkStatus[0] == 0) {
            // Could not link to program
            glDeleteProgram(programObjectID);
            return 0;
        }

        return programObjectID;
    }

    public static int compileVertexShader(String code) {
        return compileShader(GL_VERTEX_SHADER, code);
    }

    public static int compileFragmentShader(String code) {
        return compileShader(GL_FRAGMENT_SHADER, code);
    }

    public static int buildProgram(String vertexShaderSource, String fragmentShaderSource) {
        int program;

        int vertexShader = compileVertexShader(vertexShaderSource);
        int fragmentShader = compileFragmentShader(fragmentShaderSource);

        program = linkProgram(vertexShader, fragmentShader);

        if (!validateProgram(program)) {
            return 0;
        }

        return program;
    }
}