Opengl ES系列学习--蜗牛

     今天的这个蜗牛真是太猛了，计算量超大，GPU直接拉到最高频，而且负载99%！！这是什么样的计算量，我们相机使用Opengl ES平时绘制的预览，GPU是最低频，而且负载也只有3%--10%左右，看来我们的技术还不够深，要能真正实现一个功能，正常使用GPU达到这样的频率的话，那才能突显出一定的水平。来看下蜗牛的效果。

     GlSnailRender类的完整源码如下：

package com.opengl.learn.aric;

import android.content.Context;
import android.opengl.GLES32;
import android.opengl.GLSurfaceView;
import android.util.Log;

import com.opengl.learn.OpenGLUtils;
import com.opengl.learn.R;

import java.nio.ByteBuffer;
import java.nio.ByteOrder;
import java.nio.FloatBuffer;

import javax.microedition.khronos.egl.EGLConfig;
import javax.microedition.khronos.opengles.GL10;

import static android.opengl.GLES20.GL_ARRAY_BUFFER;
import static android.opengl.GLES20.GL_COLOR_BUFFER_BIT;
import static android.opengl.GLES20.GL_DEPTH_BUFFER_BIT;
import static android.opengl.GLES20.GL_DEPTH_TEST;
import static android.opengl.GLES20.GL_FLOAT;
import static android.opengl.GLES20.GL_STATIC_DRAW;
import static android.opengl.GLES20.GL_TEXTURE0;
import static android.opengl.GLES20.GL_TEXTURE1;
import static android.opengl.GLES20.GL_TEXTURE2;
import static android.opengl.GLES20.GL_TEXTURE_2D;
import static android.opengl.GLES20.GL_TRIANGLES;
import static android.opengl.GLES20.glGenBuffers;
import static android.opengl.GLES20.glGetUniformLocation;

public class GlSnailRender implements GLSurfaceView.Renderer {
    private static final String TAG = GlSnailRender.class.getSimpleName();
    private final float[] mVerticesData =
            {
                    -1.0f, 1.0f, 0.0f,
                    -1.0f, -1.0f, 0.0f,
                    1.0f, -1.0f, 0.0f,

                    1.0f, -1.0f, 0.0f,
                    1.0f, 1.0f, 0.0f,
                    -1.0f, 1.0f, 0.0f,
            };

    private static final int BYTES_PER_FLOAT = 4;
    private static final int POSITION_COMPONENT_COUNT = 3;
    private Context mContext;
    private FloatBuffer mVerticesBuffer;
    private int mProgramObject, mVAO, mVBO, iTime, iResolution;
    private int iChannel1, channel1, iChannel2, channel2, iChannel3, channel3;
    private int mWidth, mHeight;
    private long startTime;

    public GlSnailRender(Context context) {
        mContext = context;
        mVerticesBuffer = ByteBuffer.allocateDirect(mVerticesData.length * BYTES_PER_FLOAT)
                .order(ByteOrder.nativeOrder()).asFloatBuffer();
        mVerticesBuffer.put(mVerticesData).position(0);
    }

    @Override
    public void onSurfaceCreated(GL10 gl, EGLConfig config) {
        mProgramObject = OpenGLUtils.loadProgram(mContext, R.raw.glsea_vertex, R.raw.glsnail_fragment);
        iResolution = glGetUniformLocation(mProgramObject, "iResolution");
        iTime = glGetUniformLocation(mProgramObject, "iTime");
        iChannel1 = glGetUniformLocation(mProgramObject, "iChannel1");
        iChannel2 = glGetUniformLocation(mProgramObject, "iChannel2");
        iChannel3 = glGetUniformLocation(mProgramObject, "iChannel3");

        int[] array = new int[1];
        GLES32.glGenVertexArrays(array.length, array, 0);
        mVAO = array[0];
        array = new int[1];
        glGenBuffers(array.length, array, 0);
        mVBO = array[0];
        Log.e(TAG, "onSurfaceCreated, " + mProgramObject + ", uTime: " + iTime + ", uResolution: " + iResolution);

        GLES32.glBindVertexArray(mVAO);

        mVerticesBuffer.position(0);
        GLES32.glBindBuffer(GL_ARRAY_BUFFER, mVBO);
        GLES32.glBufferData(GL_ARRAY_BUFFER, BYTES_PER_FLOAT * mVerticesData.length, mVerticesBuffer, GL_STATIC_DRAW);
        GLES32.glVertexAttribPointer(0, POSITION_COMPONENT_COUNT, GL_FLOAT, false, 0, 0);
        GLES32.glEnableVertexAttribArray(0);

        channel1 = OpenGLUtils.loadTexture(mContext, R.mipmap.snail_channel1);
        channel2 = OpenGLUtils.loadTexture(mContext, R.mipmap.snail_channel2);
        channel3 = OpenGLUtils.loadTexture(mContext, R.mipmap.snail_channel3);
    }

    @Override
    public void onSurfaceChanged(GL10 gl, int width, int height) {
        mWidth = width;
        mHeight = height;
    }

    @Override
    public void onDrawFrame(GL10 gl) {
        long now = System.currentTimeMillis();

        if (startTime == 0) {
            startTime = now;
        }

        float time = (now - startTime) / (1000f * 5f);

        GLES32.glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
        GLES32.glClearColor(1.0f, 1.0f, 1.0f, 1.0f);
        GLES32.glEnable(GL_DEPTH_TEST);

        GLES32.glUseProgram(mProgramObject);
        GLES32.glUniform1f(iTime, time);
        GLES32.glUniform2f(iResolution, mWidth, mHeight);

        GLES32.glActiveTexture(GL_TEXTURE0);
        GLES32.glBindTexture(GL_TEXTURE_2D, channel1);
        GLES32.glUniform1i(iChannel1, 0);

        GLES32.glActiveTexture(GL_TEXTURE1);
        GLES32.glBindTexture(GL_TEXTURE_2D, channel2);
        GLES32.glUniform1i(iChannel2, 1);

        GLES32.glActiveTexture(GL_TEXTURE2);
        GLES32.glBindTexture(GL_TEXTURE_2D, channel3);
        GLES32.glUniform1i(iChannel3, 2);

        GLES32.glEnableVertexAttribArray(0);
        GLES32.glBindVertexArray(mVAO);
        GLES32.glDrawArrays(GL_TRIANGLES, 0, mVerticesData.length);

        GLES32.glBindVertexArray(0);
        GLES32.glDisableVertexAttribArray(0);
    }
}

     重点还是在片段着色器，网上有些说法也叫像素着色器，不过两个的重点不一样，片段着色器的重点是FragColor；像素着色器的重点是gl_FragCoord，一个变量就可以展开无数种炫丽的效果，像素着色器的魔法也就在gl_FragCoord内建变量中了。片段着色器的源码如下：

// Created by inigo quilez - 2015
// License Creative Commons Attribution-NonCommercial-ShareAlike 3.0

// You can buy a metal print of this shader here:
// https://www.redbubble.com/i/metal-print/Snail-by-InigoQuilez/39845499.0JXQP

#version 320 es
#ifdef GL_FRAGMENT_PRECISION_HIGH
precision highp float;
#else
precision mediump float;
#endif

// antialiasing - make AA 2, meaning 4x AA, if you have a fast machine
#define AA 1
#define ZERO (min(2, 0)