src/third_party/skia/platform_tools/android/apps/skar_java/src/main/java/com/google/skar/examples/helloskar/rendering/ShaderUtil.java

/*
 * Copyright 2018 Google LLC All Rights Reserved.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.skar.examples.helloskar.rendering;

import android.content.Context;
import android.opengl.GLES20;
import android.util.Log;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;

/**
 * Shader helper functions.
 */
public class ShaderUtil {
    /**
     * Converts a raw text file, saved as a resource, into an OpenGL ES shader.
     *
     * @param type     The type of shader we will be creating.
     * @param filename The filename of the asset file about to be turned into a shader.
     * @return The shader object handler.
     */
    public static int loadGLShader(String tag, Context context, int type, String filename)
            throws IOException {
        String code = readRawTextFileFromAssets(context, filename);
        int shader = GLES20.glCreateShader(type);
        GLES20.glShaderSource(shader, code);
        GLES20.glCompileShader(shader);

        // Get the compilation status.
        final int[] compileStatus = new int[1];
        GLES20.glGetShaderiv(shader, GLES20.GL_COMPILE_STATUS, compileStatus, 0);

        // If the compilation failed, delete the shader.
        if (compileStatus[0] == 0) {
            Log.e(tag, "Error compiling shader: " + GLES20.glGetShaderInfoLog(shader));
            GLES20.glDeleteShader(shader);
            shader = 0;
        }

        if (shader == 0) {
            throw new RuntimeException("Error creating shader.");
        }

        return shader;
    }

    /**
     * Checks if we've had an error inside of OpenGL ES, and if so what that error is.
     *
     * @param label Label to report in case of error.
     * @throws RuntimeException If an OpenGL error is detected.
     */
    public static void checkGLError(String tag, String label) {
        int lastError = GLES20.GL_NO_ERROR;
        // Drain the queue of all errors.
        int error;
        while ((error = GLES20.glGetError()) != GLES20.GL_NO_ERROR) {
            Log.e(tag, label + ": glError " + error);
            lastError = error;
        }
        if (lastError != GLES20.GL_NO_ERROR) {
            throw new RuntimeException(label + ": glError " + lastError);
        }
    }

    /**
     * Converts a raw text file into a string.
     *
     * @param filename The filename of the asset file about to be turned into a shader.
     * @return The context of the text file, or null in case of error.
     */
    private static String readRawTextFileFromAssets(Context context, String filename)
            throws IOException {
        try (InputStream inputStream = context.getAssets().open(filename);
             BufferedReader reader = new BufferedReader(new InputStreamReader(inputStream))) {
            StringBuilder sb = new StringBuilder();
            String line;
            while ((line = reader.readLine()) != null) {
                sb.append(line).append("\n");
            }
            return sb.toString();
        }
    }
}