据我了解，从 GLES30 开始，不再有 gl_FragColor 缓冲区(我看到了 HERE)

既然我无法读取“特殊变量”，我该如何读取“输出”缓冲区？

这是我的代码:

private static final String FRAGMENT_SHADER =
        "#version 300 es\n"+
        "#extension GL_OES_EGL_image_external_essl3 : require\n" +
        "precision mediump float;\n" +      // highp here doesn't seem to matter
        "in vec2 vTextureCoord;\n" +
        "uniform sampler2D sTexture;\n" +
        "out vec4 fragColor ;\n" +
        "void main() {\n" +
        "    vec4 tc = texture(sTexture, vTextureCoord);\n" +
        "    fragColor.r = tc.r * 0.3 + tc.g * 0.59 + tc.b * 0.11;\n" +
        "    fragColor.g = tc.r * 0.3 + tc.g * 0.59 + tc.b * 0.11;\n" +
        "    fragColor.b = tc.r * 0.3 + tc.g * 0.59 + tc.b * 0.11;\n" +
        "}\n";

这里我尝试读取数据:

 ByteBuffer mPixelBuf = ByteBuffer.allocateDirect(mWidth * mHeight * 4);
            mPixelBuf.order(ByteOrder.LITTLE_ENDIAN);

GLES30.glReadPixels(startX, startY, frameWidth, frameHeight, GLES30.GL_RGBA, GLES30.GL_UNSIGNED_BYTE, mPixelBuf);

代码中没有gl错误。

输出 mPixelBuf 只有零。

如何确保 fragColor 正在读取？

谢谢

Update1-全纹理渲染代码:

package com.MES.YOtm.AnalyzingAdapter;

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

import android.graphics.SurfaceTexture;
import android.opengl.GLES11Ext;
import android.opengl.GLES30;
import android.opengl.Matrix;
import android.util.Log;

/**
 * Code for rendering a texture onto a surface using OpenGL ES 2.0.
 */
public class STextureRender {

    private static final String TAG = "Myopengl";
    private int zoom;
    private static final int FLOAT_SIZE_BYTES = 4;
    private static final int TRIANGLE_VERTICES_DATA_STRIDE_BYTES = 5 * FLOAT_SIZE_BYTES;
    private static final int TRIANGLE_VERTICES_DATA_POS_OFFSET = 0;
    private static final int TRIANGLE_VERTICES_DATA_UV_OFFSET = 3;
    private final float[] mTriangleVerticesData = {
            // X, Y, Z, U, V
            -1.0f, -1.0f, 0, 0.f, 0.f,
             1.0f, -1.0f, 0, 1.f, 0.f,
            -1.0f,  1.0f, 0, 0.f, 1.f,
             1.0f,  1.0f, 0, 1.f, 1.f,
    };

    private FloatBuffer mTriangleVertices;


    private static final String VERTEX_SHADER =
            "#version 300 es\n"+
            "uniform mat4 uMVPMatrix;\n" +
            "uniform mat4 uSTMatrix;\n" +
            "in  vec4 aPosition;\n" +
            "in  vec4 aTextureCoord;\n" +
            "out vec2 vTextureCoord;\n" +
            "void main() {\n" +
            "    gl_Position = uMVPMatrix * aPosition;\n" +
            "    vTextureCoord = (uSTMatrix * aTextureCoord).xy;\n" +
            "}\n";
//Smapler2D
    private static final String FRAGMENT_SHADER =
            "#version 300 es\n"+
            "#extension GL_OES_EGL_image_external_essl3 : require\n" +
            "precision mediump float;\n" +      // highp here doesn't seem to matter
            "in vec2 vTextureCoord;\n" +
            "uniform mediump sampler2D sTexture;\n" +
            "layout(location = 0)  out mediump vec4 fragColor ;\n" +
            "void main() {\n" +
            "    vec4 tc = texture(sTexture, vTextureCoord);\n" +
            "    fragColor.r = tc.r * 0.3 + tc.g * 0.59 + tc.b * 0.11;\n" +
            "    fragColor.g = tc.r * 0.3 + tc.g * 0.59 + tc.b * 0.11;\n" +
            "    fragColor.b = tc.r * 0.3 + tc.g * 0.59 + tc.b * 0.11;\n" +
            "}\n";



    private float[] mMVPMatrix = new float[16];
    private float[] mSTMatrix = new float[16];

    private int mProgram;
    private int mTextureID = -12345;
    private int muMVPMatrixHandle;
    private int muSTMatrixHandle;
    private int maPositionHandle;
    private int maTextureHandle;

    public STextureRender(int _zoom) {
        Log.v("My Error", "Start STextureRender constructor");
        try
        {

            mTriangleVertices = ByteBuffer.allocateDirect(
                    mTriangleVerticesData.length * FLOAT_SIZE_BYTES)
                    .order(ByteOrder.nativeOrder()).asFloatBuffer();
            mTriangleVertices.put(mTriangleVerticesData).position(0);

            Matrix.setIdentityM(mSTMatrix, 0);
            zoom = _zoom;
       }
       catch(Exception ex)
       {
           Log.v("My Error", "STextureRender Error = " + ex.toString());
       }
        Log.v("My Error", "End STextureRender constructor");
    }

    public int getTextureId() {
        return mTextureID;
    }

    /**
     * Draws the external texture in SurfaceTexture onto the current EGL surface.
     */
    public void drawFrame(SurfaceTexture st, boolean invert) {
        checkGlError("onDrawFrame start");
        try
        {
            st.getTransformMatrix(mSTMatrix);
            if (invert) {
                mSTMatrix[5] = -mSTMatrix[5];
                mSTMatrix[13] = 1.0f - mSTMatrix[13];
            }

            GLES30.glClearColor(0.0f, 1.0f, 0.0f, 1.0f);
            GLES30.glClear(GLES30.GL_COLOR_BUFFER_BIT);

            GLES30.glUseProgram(mProgram);
            checkGlError("glUseProgram");

            GLES30.glActiveTexture(GLES30.GL_TEXTURE0);
            GLES30.glBindTexture(GLES11Ext.GL_TEXTURE_EXTERNAL_OES, mTextureID);

            mTriangleVertices.position(TRIANGLE_VERTICES_DATA_POS_OFFSET);
            GLES30.glVertexAttribPointer(maPositionHandle, 3, GLES30.GL_FLOAT, false,
                    TRIANGLE_VERTICES_DATA_STRIDE_BYTES, mTriangleVertices);
            checkGlError("glVertexAttribPointer maPosition");
            GLES30.glEnableVertexAttribArray(maPositionHandle);
            checkGlError("glEnableVertexAttribArray maPositionHandle");

            mTriangleVertices.position(TRIANGLE_VERTICES_DATA_UV_OFFSET);
            GLES30.glVertexAttribPointer(maTextureHandle, 2, GLES30.GL_FLOAT, false,
                    TRIANGLE_VERTICES_DATA_STRIDE_BYTES, mTriangleVertices);
            checkGlError("glVertexAttribPointer maTextureHandle");
            GLES30.glEnableVertexAttribArray(maTextureHandle);
            checkGlError("glEnableVertexAttribArray maTextureHandle");

            Matrix.setIdentityM(mMVPMatrix, 0);
            GLES30.glUniformMatrix4fv(muMVPMatrixHandle, 1, false, mMVPMatrix, 0);
            GLES30.glUniformMatrix4fv(muSTMatrixHandle, 1, false, mSTMatrix, 0);

            GLES30.glDrawArrays(GLES30.GL_TRIANGLE_STRIP, 0, 4);
            checkGlError("glDrawArrays");
       }
       catch(Exception ex)
       {
           Log.v("My Error", "drawFrame Error = " + ex.toString());
       }
    }

    /**
     * Initializes GL state.  Call this after the EGL surface has been created and made current.
     */
    public void surfaceCreated() {
        try
        {
            mProgram = createProgram(VERTEX_SHADER, FRAGMENT_SHADER);
            if (mProgram == 0) {
                throw new RuntimeException("failed creating program");
            }
            maPositionHandle = GLES30.glGetAttribLocation(mProgram, "aPosition");
            checkGlError("glGetAttribLocation aPosition");
            if (maPositionHandle == -1) {
                throw new RuntimeException("Could not get attrib location for aPosition");
            }
            maTextureHandle = GLES30.glGetAttribLocation(mProgram, "aTextureCoord");
            checkGlError("glGetAttribLocation aTextureCoord");
            if (maTextureHandle == -1) {
                throw new RuntimeException("Could not get attrib location for aTextureCoord");
            }

            muMVPMatrixHandle = GLES30.glGetUniformLocation(mProgram, "uMVPMatrix");
            checkGlError("glGetUniformLocation uMVPMatrix");
            if (muMVPMatrixHandle == -1) {
                throw new RuntimeException("Could not get attrib location for uMVPMatrix");
            }

            muSTMatrixHandle = GLES30.glGetUniformLocation(mProgram, "uSTMatrix");
            checkGlError("glGetUniformLocation uSTMatrix");
            if (muSTMatrixHandle == -1) {
                throw new RuntimeException("Could not get attrib location for uSTMatrix");
            }

            int[] textures = new int[1];
            GLES30.glGenTextures(1, textures, 0);

            mTextureID = textures[0];
            GLES30.glBindTexture(GLES11Ext.GL_TEXTURE_EXTERNAL_OES, mTextureID);
            checkGlError("glBindTexture mTextureID");

            GLES30.glTexParameterf(GLES11Ext.GL_TEXTURE_EXTERNAL_OES, GLES30.GL_TEXTURE_MIN_FILTER,
                    GLES30.GL_NEAREST);
            GLES30.glTexParameterf(GLES11Ext.GL_TEXTURE_EXTERNAL_OES, GLES30.GL_TEXTURE_MAG_FILTER,
                    GLES30.GL_LINEAR);
            GLES30.glTexParameteri(GLES11Ext.GL_TEXTURE_EXTERNAL_OES, GLES30.GL_TEXTURE_WRAP_S,
                    GLES30.GL_CLAMP_TO_EDGE);
            GLES30.glTexParameteri(GLES11Ext.GL_TEXTURE_EXTERNAL_OES, GLES30.GL_TEXTURE_WRAP_T,
                    GLES30.GL_CLAMP_TO_EDGE);
            checkGlError("glTexParameter");
       }
       catch(Exception ex)
       {
           Log.v("My Error", "surfaceCreated Error = " + ex.toString());
       }
    }

    /**
     * Replaces the fragment shader.  Pass in null to reset to default.
     */
    public void changementShader(String fragmentShader) {
        try
        {
        if (fragmentShader == null) {
            fragmentShader = FRAGMENT_SHADER;
        }
        GLES30.glDeleteProgram(mProgram);
        mProgram = createProgram(VERTEX_SHADER, fragmentShader);
        if (mProgram == 0) {
            Log.v("My Error", "failed creating program");
            throw new RuntimeException("failed creating program");
        }
       }
       catch(Exception ex)
       {
           Log.v("My Error", " changementShader Error = " + ex.toString());
       }
    }

    private int loadShader(int shaderType, String source) {
        try
        {
            int shader = GLES30.glCreateShader(shaderType);
            checkGlError("glCreateShader type=" + shaderType);

            GLES30.glShaderSource(shader, source);
            GLES30.glCompileShader(shader);
            int[] compiled = new int[1];
            GLES30.glGetShaderiv(shader, GLES30.GL_COMPILE_STATUS, compiled, 0);
            if (compiled[0] == 0) {
                Log.e(TAG, "Could not compile shader " + shaderType + ":");
                Log.e(TAG, " " + GLES30.glGetShaderInfoLog(shader));
                GLES30.glDeleteShader(shader);
                shader = 0;
            }

            return shader;
       }
       catch(Exception ex)
       {
           Log.v("My Error", "loadShader Error = " + ex.toString());
           return 0;
       }
    }

    private int createProgram(String vertexSource, String fragmentSource) {
        try
        {
            int vertexShader = loadShader(GLES30.GL_VERTEX_SHADER, vertexSource);
            if (vertexShader == 0) {
                return 0;
            }
            int pixelShader = loadShader(GLES30.GL_FRAGMENT_SHADER, fragmentSource);
            if (pixelShader == 0) {
                return 0;
            }

            int program = GLES30.glCreateProgram();
            checkGlError("glCreateProgram");
            if (program == 0) {
                Log.e(TAG, "Could not create program");
            }
            GLES30.glAttachShader(program, vertexShader);
            checkGlError("glAttachShader");
            GLES30.glAttachShader(program, pixelShader);
            checkGlError("glAttachShader");
            GLES30.glLinkProgram(program);
            int[] linkStatus = new int[1];
            GLES30.glGetProgramiv(program, GLES30.GL_LINK_STATUS, linkStatus, 0);
            if (linkStatus[0] != GLES30.GL_TRUE) {
                Log.e(TAG, "Could not link program: ");
                Log.e(TAG, GLES30.glGetProgramInfoLog(program));
                GLES30.glDeleteProgram(program);
                program = 0;
            }
            return program;
       }
       catch(Exception ex)
       {
           Log.v("My Error", "createProgram Error = " + ex.toString());
           return 0;
       }
    }

    public void checkGlError(String op) {
        int error;
        while ((error = GLES30.glGetError()) != GLES30.GL_NO_ERROR) {
            Log.e(TAG, op + ": glError " + error);
            throw new RuntimeException(op + ": glError " + error);
        }
    }
}

最佳答案

您的着色器代码与 glReadPixels 读取的内容完全无关，也与特殊变量名无关。它从当前绑定(bind)的读取帧缓冲区中读取；即 glReadPixels 在 ES 3.0 中的工作方式与它在 ES 2.0 中的工作方式完全相同。

唯一的异常(exception)是多渲染目标支持，但这与本例无关。

How can I make sure that fragColor is reading?

glClearColor(some interesting color)
glClear(COLOR_BUFFER_BIT)
glReadPixels()
assert color == some interesting color

关于android - 如何在 Android 上使用基于 GLES30 的 glreadpixels 从特定缓冲区读取数据，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/39506470/