1 前言
本文通过一个立方体贴图的例子，讲解三维纹理贴图的应用，案例中使用 6 张不同的图片给立方体贴图，图片如下：
本文涉及到的知识点主要包含：三维绘图、MVP 矩阵变换、纹理贴图，读者如果对 OpenGL ES 不太熟悉，请回顾以下内容：
本文完整代码资源见→ 【OpenGL ES】立方体贴图（6张图）
项目目录如下：
2 案例
MainActivity.java
package com.zhyan8.texture3d;
import android.opengl.GLSurfaceView;
import android.os.Bundle;
import androidx.appcompat.app.AppCompatActivity;
public class MainActivity extends AppCompatActivity {
private GLSurfaceView mGlSurfaceView;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
mGlSurfaceView = new MyGLSurfaceView(this);
setContentView(mGlSurfaceView);
mGlSurfaceView.setRenderer(new MyRender(this));
}
@Override
protected void onResume() {
super.onResume();
mGlSurfaceView.onResume();
}
@Override
protected void onPause() {
super.onPause();
mGlSurfaceView.onPause();
}
}
MyGLSurfaceView.java
package com.zhyan8.texture3d;
import android.content.Context;
import android.opengl.GLSurfaceView;
import android.util.AttributeSet;
public class MyGLSurfaceView extends GLSurfaceView {
public MyGLSurfaceView(Context context) {
super(context);
setEGLContextClientVersion(3);
}
public MyGLSurfaceView(Context context, AttributeSet attrs) {
super(context, attrs);
setEGLContextClientVersion(3);
}
}
MyRender.java
package com.zhyan8.texture3d;
import android.content.Context;
import android.opengl.GLES30;
import android.opengl.GLSurfaceView;
import java.nio.FloatBuffer;
import javax.microedition.khronos.egl.EGLConfig;
import javax.microedition.khronos.opengles.GL10;
public class MyRender implements GLSurfaceView.Renderer {
private FloatBuffer vertexBuffer;
private FloatBuffer textureBuffer;
private MyGLUtils mGLUtils;
private int mProgramId;
private float mRatio;
private int[] mTextureIds;
public MyRender(Context context) {
mGLUtils = new MyGLUtils(context);
}
@Override
public void onSurfaceCreated(GL10 gl, EGLConfig eglConfig) {
//设置背景颜色
GLES30.glClearColor(0.1f, 0.2f, 0.3f, 0.4f);
//启动深度测试
gl.glEnable(GLES30.GL_DEPTH_TEST);
//编译着色器
final int vertexShaderId = mGLUtils.compileShader(GLES30.GL_VERTEX_SHADER, R.raw.vertex_shader);
final int fragmentShaderId = mGLUtils.compileShader(GLES30.GL_FRAGMENT_SHADER, R.raw.fragment_shader);
//链接程序片段
mProgramId = mGLUtils.linkProgram(vertexShaderId, fragmentShaderId);
GLES30.glUseProgram(mProgramId);
mTextureIds = mGLUtils.loadTexture(Model.resIds);
}
@Override
public void onSurfaceChanged(GL10 gl, int width, int height) {
//设置视图窗口
GLES30.glViewport(0, 0, width, height);
getFloatBuffer();
mRatio = 1.0f * width / height;
}
@Override
public void onDrawFrame(GL10 gl) {
//将颜色缓冲区设置为预设的颜色
GLES30.glClear(GLES30.GL_COLOR_BUFFER_BIT | GLES30.GL_DEPTH_BUFFER_BIT);
mGLUtils.transform(mProgramId, mRatio); //计算MVP变换矩阵
//启用顶点的数组句柄
GLES30.glEnableVertexAttribArray(0);
GLES30.glEnableVertexAttribArray(1);
//准备顶点坐标和纹理坐标
GLES30.glVertexAttribPointer(0, 3, GLES30.GL_FLOAT, false, 0, vertexBuffer);
GLES30.glVertexAttribPointer(1, 2, GLES30.GL_FLOAT, false, 0, textureBuffer);
//激活纹理
GLES30.glActiveTexture(GLES30.GL_TEXTURE);
//绘制纹理
drawTextures();
//禁止顶点数组句柄
GLES30.glDisableVertexAttribArray(0);
GLES30.glDisableVertexAttribArray(1);
}
private void getFloatBuffer() {
vertexBuffer = mGLUtils.getFloatBuffer(Model.vertex);
textureBuffer = mGLUtils.getFloatBuffer(Model.texture);
}
private void drawTextures() {
int count = 4;
for (int i =0; i < mTextureIds.length; i++) {
int first = i * count;
//绑定纹理
GLES30.glBindTexture(GLES30.GL_TEXTURE_2D, mTextureIds[i]);
//绘制正方体的表面（6个面，每个面2个三角形）
GLES30.glDrawArrays(GLES30.GL_TRIANGLE_FAN, first, count);
}
}
}
GLUtils.java
package com.zhyan8.texture3d;
import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.opengl.GLES30;
import android.opengl.GLUtils;
import android.opengl.Matrix;
import java.io.BufferedReader;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.nio.ByteBuffer;
import java.nio.ByteOrder;
import java.nio.FloatBuffer;
public class MyGLUtils {
private Context mContext;
private int mRotateAgree = 0;
public MyGLUtils(Context context) {
mContext = context;
}
public FloatBuffer getFloatBuffer(float[] floatArr) {
FloatBuffer fb = ByteBuffer.allocateDirect(floatArr.length * Float.BYTES)
.order(ByteOrder.nativeOrder())
.asFloatBuffer();
fb.put(floatArr);
fb.position(0);
return fb;
}
//通过代码片段编译着色器
public int compileShader(int type, String shaderCode){
int shader = GLES30.glCreateShader(type);
GLES30.glShaderSource(shader, shaderCode);
GLES30.glCompileShader(shader);
return shader;
}
//通过外部资源编译着色器
public int compileShader(int type, int shaderId){
String shaderCode = readShaderFromResource(shaderId);
return compileShader(type, shaderCode);
}
//链接到着色器
public int linkProgram(int vertexShaderId, int fragmentShaderId) {
final int programId = GLES30.glCreateProgram();
//将顶点着色器加入到程序
GLES30.glAttachShader(programId, vertexShaderId);
//将片元着色器加入到程序
GLES30.glAttachShader(programId, fragmentShaderId);
//链接着色器程序
GLES30.glLinkProgram(programId);
return programId;
}
//从shader文件读出字符串
private String readShaderFromResource(int shaderId) {
InputStream is = mContext.getResources().openRawResource(shaderId);
BufferedReader br = new BufferedReader(new InputStreamReader(is));
String line;
StringBuilder sb = new StringBuilder();
try {
while ((line = br.readLine()) != null) {
sb.append(line);
sb.append("\n");
}
br.close();
} catch (Exception e) {
e.printStackTrace();
}
return sb.toString();
}
//加载纹理贴图
public int[] loadTexture(int[] resIds) {
BitmapFactory.Options options = new BitmapFactory.Options();
options.inScaled = false;
Bitmap[] bitmaps = new Bitmap[resIds.length];
// 生成纹理id
final int[] textureIds = new int[resIds.length];
GLES30.glGenTextures(resIds.length, textureIds, 0);
for (int i = 0; i < resIds.length; i++) {
bitmaps[i] = BitmapFactory.decodeResource(mContext.getResources(), resIds[i], options);
// 绑定纹理到OpenGL
GLES30.glBindTexture(GLES30.GL_TEXTURE_2D, textureIds[i]);
GLES30.glTexParameteri(GLES30.GL_TEXTURE_2D, GLES30.GL_TEXTURE_MIN_FILTER, GLES30.GL_LINEAR_MIPMAP_LINEAR);
GLES30.glTexParameteri(GLES30.GL_TEXTURE_2D, GLES30.GL_TEXTURE_MAG_FILTER, GLES30.GL_LINEAR);
// 加载bitmap到纹理中
GLUtils.texImage2D(GLES30.GL_TEXTURE_2D, 0, bitmaps[i], 0);
// 生成MIP贴图
GLES30.glGenerateMipmap(GLES30.GL_TEXTURE_2D);
// 取消绑定纹理
GLES30.glBindTexture(GLES30.GL_TEXTURE_2D, 0);
bitmaps[i].recycle();
}
return textureIds;
}
//计算MVP变换矩阵
public void transform(int programId, float ratio) {
//初始化modelMatrix, viewMatrix, projectionMatrix
float[] modelMatrix = getIdentityMatrix(16, 0); //模型变换矩阵
float[] viewMatrix = getIdentityMatrix(16, 0); //观测变换矩阵
float[] projectionMatrix = getIdentityMatrix(16, 0); //投影变换矩阵
//获取modelMatrix, viewMatrix, projectionMatrix
mRotateAgree = (mRotateAgree + 2) % 360;
Matrix.rotateM(modelMatrix, 0, mRotateAgree, -1, -1, 1); //获取模型旋转变换矩阵
Matrix.setLookAtM(viewMatrix, 0, 0, 5, 10, 0, 0, 0, 0, 1, 0); //获取观测变换矩阵
Matrix.frustumM(projectionMatrix, 0, -ratio, ratio, -1, 1, 3, 20); //获取投影变换矩阵
//计算MVP变换矩阵: mvpMatrix = projectionMatrix * viewMatrix * modelMatrix
float[] tempMatrix = new float[16];
float[] mvpMatrix = new float[16];
Matrix.multiplyMM(tempMatrix, 0, viewMatrix, 0, modelMatrix, 0);
Matrix.multiplyMM(mvpMatrix, 0, projectionMatrix, 0, tempMatrix, 0);
//设置MVP变换矩阵
int mvpMatrixHandle = GLES30.glGetUniformLocation(programId, "mvpMatrix");
GLES30.glUniformMatrix4fv(mvpMatrixHandle, 1, false, mvpMatrix, 0);
}
private float[] getIdentityMatrix(int size, int offset) {
float[] matrix = new float[size];
Matrix.setIdentityM(matrix, offset);
return matrix;
}
}
Model.java
package com.zhyan8.texture3d;
public class Model {
private static float r = 1.0f;
public static int[] resIds = new int[] {
R.raw.x1, R.raw.x2, R.raw.x3,
R.raw.x4, R.raw.x5, R.raw.x6
};
public static float[] vertex = new float[] {
//前面
r, r, r,
-r, r, r,
-r, -r, r,
r, -r, r,
//后面
r, r, -r,
-r, r, -r,
-r, -r, -r,
r, -r, -r,
//上面
r, r, r,
r, r, -r,
-r, r, -r,
-r, r, r,
//下面
r, -r, r,
r, -r, -r,
-r, -r, -r,
-r, -r, r,
//右面
r, r, r,
r, r, -r,
r, -r, -r,
r, -r, r,
//左面
-r, r, r,
-r, r, -r,
-r, -r, -r,
-r, -r, r
};
public static float[] texture = new float[] {
//前面
0f, 0f,
1f, 0f,
1f, 1f,
0f, 1f,
//后面
0f, 0f,
1f, 0f,
1f, 1f,
0f, 1f,
//上面
0f, 0f,
1f, 0f,
1f, 1f,
0f, 1f,
//下面
0f, 0f,
1f, 0f,
1f, 1f,
0f, 1f,
//右面
0f, 0f,
1f, 0f,
1f, 1f,
0f, 1f,
//左面
0f, 0f,
1f, 0f,
1f, 1f,
0f, 1f
};
}
vertex_shader.glsl
#version 300 es
layout (location = 0) in vec4 vPosition;
layout (location = 1) in vec2 aTextureCoord;
uniform mat4 mvpMatrix;
out vec2 vTexCoord;
void main() {
gl_Position = mvpMatrix * vPosition;
vTexCoord = aTextureCoord;
}
顶点着色器的作用：进行矩阵变换位置、根据光照公式计算顶点颜⾊、⽣成 / 变换纹理坐标，并且把位置和纹理坐标发送到片元着色器。
顶点着色器中，如果没有指定默认精度，则 int 和 float 的默认精度都为 highp。
fragment_shader.glsl
#version 300 es
precision mediump float;
uniform sampler2D uTextureUnit;
in vec2 vTexCoord;
out vec4 fragColor;
void main() {
fragColor = texture(uTextureUnit,vTexCoord);
}
片元着色器的作用：处理经光栅化阶段生成的每个片元，计算每个像素的颜色和透明度。
在片元着色器中，浮点值没有默认的精度值，每个着色器必须声明一个默认的 float 精度。
运行效果：
声明：本文转自【OpenGL ES】立方体贴图（6张图）
