NDK OpenGL ES 3.0 开发(十六):相机预览

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OpenGL ES 相机预览

OpenGL ES 相机预览

相机开发是 OpenGL ES 的重要应用,利用 OpenGL 可以很方便地实现相机美颜、滤镜、塑型以及一些动态特效,其性能显著优于对应功能的 CPU 实现。

相机的预览实现一般有 2 种方式,一种是基于 Android 原生 SurfaceTexture 的纯 GPU 实现方式,另一种是通过相机的预览回调接口获取帧的 YUV 数据,利用 CPU 算法处理完成之后,传入显存,再利用 GPU 实现 YUV 转 RGBA 进行渲染,即 CPU + GPU 的实现方式。

基于 Android 原生 SurfaceTexture 的纯 GPU 实现方式,相机可以使用 SurfaceTexture 作为预览载体,SurfaceTexture 可来自于 GLSurfaceView、TextureView 或 SurfaceView 这些独立拥有 Surface 的封装类,也可以自定义实现。

作为预览载体的 SurfaceTexture 绑定的纹理需要是 OES 纹理,即 GLES11Ext.GL_TEXTURE_EXTERNAL_OES 纹理,来自于 GLES 的扩展 #extension GL_OES_EGL_image_external 中,使用 OES 纹理后,我们不需要在片段着色器中自己做 YUV to RGBA 的转换,因为 OES 纹理可以直接接收 YUV 数据或者直接输出 YUV 数据。

类似于普通 2D 纹理的创建,OES 纹理创建的实现如下:

private int createOESTexture(){
    int[] texture = new int[1];
    GLES20.glGenTextures(1, texture, 0);
    GLES20.glBindTexture(GLES11Ext.GL_TEXTURE_EXTERNAL_OES, texture[0]);
    GLES20.glTexParameterf(GLES11Ext.GL_TEXTURE_EXTERNAL_OES,
        GL10.GL_TEXTURE_MIN_FILTER,GL10.GL_LINEAR);
    GLES20.glTexParameterf(GLES11Ext.GL_TEXTURE_EXTERNAL_OES,
        GL10.GL_TEXTURE_MAG_FILTER, GL10.GL_LINEAR);
    GLES20.glTexParameteri(GLES11Ext.GL_TEXTURE_EXTERNAL_OES,
        GL10.GL_TEXTURE_WRAP_S, GL10.GL_CLAMP_TO_EDGE);
    GLES20.glTexParameteri(GLES11Ext.GL_TEXTURE_EXTERNAL_OES,
        GL10.GL_TEXTURE_WRAP_T, GL10.GL_CLAMP_TO_EDGE);
    return texture[0];
}

使用 OES 纹理需要修改片段着色器,在着色器脚本的头部增加扩展纹理的声明 #extension GL_OES_EGL_image_external : require ,并且纹理采样器不再使用 sample2D ,需要换成 samplerExternalOES 作为纹理采样器。

#version 300 es
#extension GL_OES_EGL_image_external : require
precision mediump float;
in vec2 v_texCoord;
uniform samplerExternalOES s_TexSampler;
void main() {
    gl_FragColor = texture(s_TexSampler, v_texCoord);
}

实际上当使用 TextureView 时,实际上也不需要自己去创建 OES 纹理,只需要绑定相机,配置好变换矩阵后即可实现相机预览。具体例子可直接参考Android 官方的 Samples https://github.com/android/camera-samples 。

相机预览基于 Android 原生 API 的纯 GPU 实现方式,操作简单,代码量很少,原生 API 已经做了很多封装,可以利用片段着色器轻易实现美颜滤镜等相机特效,缺点是扩展性差,例如要使用传统的 CPU 算法做一些滤镜或者美颜特效就很不方便,图像数据需要多次在内存与显存之间拷贝,会造成性能和功耗问题。

本文主要介绍将图像数据取出,传入 Native 层,然后对数据做一些处理(可选),最后再做渲染的方式,这种方式相对复杂一些。相机预览数据的常见格式是 YUV420P 或者 YUV420SP(NV21) ,需要将图像数据对应 YUV 3 个分量使用 3 个纹理传入显存,在片段着色器中将 YUV 数据转为 RGBA 。

相关原理可参考NDK OpenGL ES 3.0 开发(三):YUV 渲染 章节。

相机预览数据获取,以 Camera2 为例,主要是通过 ImageReader 实现,该类封装了 Surface :

private ImageReader.OnImageAvailableListener mOnPreviewImageAvailableListener = new ImageReader.OnImageAvailableListener() {
    @Override
    public void onImageAvailable(ImageReader reader) {
        Image image = reader.acquireLatestImage();
        if (image != null) {
            if (mCamera2FrameCallback != null) {
                mCamera2FrameCallback.onPreviewFrame(CameraUtil.YUV_420_888_data(image), image.getWidth(), image.getHeight());
            }
            image.close();
        }
    }
};

mPreviewImageReader = ImageReader.newInstance(mPreviewSize.getWidth(), mPreviewSize.getHeight(), ImageFormat.YUV_420_888, 2);
mPreviewImageReader.setOnImageAvailableListener(mOnPreviewImageAvailableListener, mBackgroundHandler);

CaptureRequest.Builder builder = mCameraDevice.createCaptureRequest(CameraDevice.TEMPLATE_PREVIEW);
builder.addTarget(mPreviewImageReader.getSurface());

session.setRepeatingRequest(mPreviewRequest, null, mBackgroundHandler);

//在自定义接口中获取预览数据,通过 JNI 传入到 C++ 层
public void onPreviewFrame(byte[] data, int width, int height) {
    Log.d(TAG, "onPreviewFrame() called with: data = [" + data + "], width = [" + width + "], height = [" + height + "]");
    mByteFlowRender.setRenderFrame(IMAGE_FORMAT_I420, data, width, height);

    //每次传入新数据,请求重新渲染
    mByteFlowRender.requestRender();
}

主要的 JNI :

public abstract class ByteFlowRender {
    public static final int GL_RENDER_TYPE = 0;
    public static final int CL_RENDER_TYPE = 1;

    public static final int IMAGE_FORMAT_RGBA = 0x01;
    public static final int IMAGE_FORMAT_NV21 = 0x02;
    public static final int IMAGE_FORMAT_NV12 = 0x03;
    public static final int IMAGE_FORMAT_I420 = 0x04;

    public static final int PARAM_TYPE_SET_SHADER_INDEX = 201;

    static {
        System.loadLibrary("byteflow_render");
    }

    private long mNativeContextHandle;

    protected native void native_CreateContext(int renderType);

    protected native void native_DestroyContext();

    protected native int native_Init(int initType);

    protected native int native_UnInit();

    protected native void native_UpdateFrame(int format, byte[] data, int width, int height);

    protected native void native_LoadFilterData(int index, int format, int width, int height, byte[] bytes);

    protected native void native_LoadShaderScript(int shaderIndex, String scriptStr);

    protected native void native_SetTransformMatrix(float translateX, float translateY, float scaleX, float scaleY, int degree, int mirror);

    protected native void native_SetParamsInt(int paramType, int value);

    protected native int native_GetParamsInt(int paramType);

    protected native void native_OnSurfaceCreated();

    protected native void native_OnSurfaceChanged(int width, int height);

    protected native void native_OnDrawFrame();
}

渲染 YUV 数据用到的着色器脚本,主要是将 3 个纹理对应的 YUV 分量,分别采样后转成 RGBA :

//顶点着色器
#version 100
varying vec2 v_texcoord;
attribute vec4 position;
attribute vec2 texcoord;
uniform mat4 MVP;
void main() {
    v_texcoord = texcoord;
    gl_Position = MVP*position;
}

//片段着色器
#version 100
precision highp float;
varying vec2 v_texcoord;
uniform lowp sampler2D s_textureY;
uniform lowp sampler2D s_textureU;
uniform lowp sampler2D s_textureV;
void main() {
    float y, u, v, r, g, b;
    y = texture2D(s_textureY, v_texcoord).r;
    u = texture2D(s_textureU, v_texcoord).r;
    v = texture2D(s_textureV, v_texcoord).r;
    u = u - 0.5;
    v = v - 0.5;
    r = y + 1.403 * v;
    g = y - 0.344 * u - 0.714 * v;
    b = y + 1.770 * u;
    gl_FragColor = vec4(r, g, b, 1.0);
}

C++ 层的主要实现:

//编译链接着色器
int GLByteFlowRender::CreateProgram(const char *pVertexShaderSource, const char *pFragShaderSource)
{
    m_Program = GLUtils::CreateProgram(pVertexShaderSource, pFragShaderSource, m_VertexShader,
                                       m_FragShader);
    if (!m_Program)
    {
        GLUtils::CheckGLError("Create Program");
        LOGCATE("GLByteFlowRender::CreateProgram Could not create program.");
        return 0;
    }

    m_YTextureHandle = glGetUniformLocation(m_Program, "s_textureY");
    m_UTextureHandle = glGetUniformLocation(m_Program, "s_textureU");
    m_VTextureHandle = glGetUniformLocation(m_Program, "s_textureV");

    m_VertexCoorHandle = (GLuint) glGetAttribLocation(m_Program, "position");
    m_TextureCoorHandle = (GLuint) glGetAttribLocation(m_Program, "texcoord");
    m_MVPHandle = glGetUniformLocation(m_Program, "MVP");

    return m_Program;
}

//创建 YUV 分量对应的 3 个纹理
bool GLByteFlowRender::CreateTextures()
{
    LOGCATE("GLByteFlowRender::CreateTextures");
    GLsizei yWidth = static_cast(m_RenderFrame.width);
    GLsizei yHeight = static_cast(m_RenderFrame.height);

    glActiveTexture(GL_TEXTURE0);
    glGenTextures(1, &m_YTextureId);
    glBindTexture(GL_TEXTURE_2D, m_YTextureId);
    glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
    glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
    glTexImage2D(GL_TEXTURE_2D, 0, GL_LUMINANCE, yWidth, yHeight, 0, GL_LUMINANCE, GL_UNSIGNED_BYTE,
                 NULL);

    if (!m_YTextureId)
    {
        GLUtils::CheckGLError("Create Y texture");
        return false;
    }

    GLsizei uWidth = static_cast(m_RenderFrame.width / 2);
    GLsizei uHeight = yHeight / 2;

    glActiveTexture(GL_TEXTURE1);
    glGenTextures(1, &m_UTextureId);
    glBindTexture(GL_TEXTURE_2D, m_UTextureId);
    glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
    glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
    glTexImage2D(GL_TEXTURE_2D, 0, GL_LUMINANCE, uWidth, uHeight, 0, GL_LUMINANCE, GL_UNSIGNED_BYTE,
                 NULL);

    if (!m_UTextureId)
    {
        GLUtils::CheckGLError("Create U texture");
        return false;
    }

    GLsizei vWidth = static_cast(m_RenderFrame.width / 2);
    GLsizei vHeight = (GLsizei) yHeight / 2;

    glActiveTexture(GL_TEXTURE2);
    glGenTextures(1, &m_VTextureId);
    glBindTexture(GL_TEXTURE_2D, m_VTextureId);
    glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
    glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
    glTexImage2D(GL_TEXTURE_2D, 0, GL_LUMINANCE, vWidth, vHeight, 0, GL_LUMINANCE, GL_UNSIGNED_BYTE,
                 NULL);

    if (!m_VTextureId)
    {
        GLUtils::CheckGLError("Create V texture");
        return false;
    }

    return true;
}

//每传入一帧新数据后,更新纹理
bool GLByteFlowRender::UpdateTextures()
{
    LOGCATE("GLByteFlowRender::UpdateTextures");
    if (m_RenderFrame.ppPlane[0] == NULL)
    {
        return false;
    }

    if (!m_YTextureId && !m_UTextureId && !m_VTextureId && !CreateTextures())
    {
        return false;
    }

    glActiveTexture(GL_TEXTURE0);
    glBindTexture(GL_TEXTURE_2D, m_YTextureId);
    glTexImage2D(GL_TEXTURE_2D, 0, GL_LUMINANCE, (GLsizei) m_RenderFrame.width,
                 (GLsizei) m_RenderFrame.height, 0,
                 GL_LUMINANCE, GL_UNSIGNED_BYTE, m_RenderFrame.ppPlane[0]);

    glActiveTexture(GL_TEXTURE1);
    glBindTexture(GL_TEXTURE_2D, m_UTextureId);
    glTexImage2D(GL_TEXTURE_2D, 0, GL_LUMINANCE, (GLsizei) m_RenderFrame.width >> 1,
                 (GLsizei) m_RenderFrame.height >> 1, 0,
                 GL_LUMINANCE, GL_UNSIGNED_BYTE, m_RenderFrame.ppPlane[1]);

    glActiveTexture(GL_TEXTURE2);
    glBindTexture(GL_TEXTURE_2D, m_VTextureId);
    glTexImage2D(GL_TEXTURE_2D, 0, GL_LUMINANCE, (GLsizei) m_RenderFrame.width >> 1,
                 (GLsizei) m_RenderFrame.height >> 1, 0,
                 GL_LUMINANCE, GL_UNSIGNED_BYTE, m_RenderFrame.ppPlane[2]);

    return true;
}

//绑定纹理到着色器,传入顶点和纹理坐标数据
GLuint GLByteFlowRender::UseProgram()
{
    LOGCATE("GLByteFlowRender::UseProgram");
    ByteFlowLock lock(&m_ShaderBufLock);
    if (m_IsShaderChanged)
    {
        GLUtils::DeleteProgram(m_Program);
        CreateProgram(kVertexShader, m_pFragShaderBuf);
        m_IsShaderChanged = false;
        m_IsProgramChanged = true;
    }


    if (!m_Program)
    {
        LOGCATE("GLByteFlowRender::UseProgram Could not use program.");
        return 0;
    }

    if (m_IsProgramChanged)
    {
        glUseProgram(m_Program);
        GLUtils::CheckGLError("GLByteFlowRender::UseProgram");

        glVertexAttribPointer(m_VertexCoorHandle, 2, GL_FLOAT, GL_FALSE, 2 * 4, VERTICES_COORS);
        glEnableVertexAttribArray(m_VertexCoorHandle);

        glUniform1i(m_YTextureHandle, 0);
        glUniform1i(m_UTextureHandle, 1);
        glUniform1i(m_VTextureHandle, 2);

        glVertexAttribPointer(m_TextureCoorHandle, 2, GL_FLOAT, GL_FALSE, 2 * 4, TEXTURE_COORS);
        glEnableVertexAttribArray(m_TextureCoorHandle);

        m_IsProgramChanged = false;
    }
    return m_Program;
}

//渲染预览图像
void GLByteFlowRender::OnDrawFrame()
{
    LOGCATE("GLByteFlowRender::OnDrawFrame");
    glViewport(0, 0, m_ViewportWidth, m_ViewportHeight);
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    glClearColor(0.0f, 0.0f, 0.0f, 1.0f);
    glDisable(GL_CULL_FACE);

    if (!UpdateTextures() || !UseProgram())
    {
        LOGCATE("GLByteFlowRender::OnDrawFrame skip frame");
        return;
    }
    glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
}

后面文章会基于该预览实现添加一些滤镜效果。

实现代码路径:
OpenGLCamera2

联系与交流

有疑问或技术交流可以添加我的微信:Byte-Flow

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