在Android上使用FBO進行緩慢的OpenGL ES渲染紋理乒乓

Question

我使用Qt進行了渲染到紋理的測試，同時在macOS和Android上運行它。 該測試創建2個紋理和一個FBO，然后在循環中將交替的紋理附加為渲染目標。 在Android上，代碼出奇地慢。 在Samsung Galaxy Tab S上，它的速度比Mac上慢30-40倍，因此我懷疑出現了問題。 片段着色器中的實際代碼似乎無關緊要。

在glBindFramebuffer之后添加glClear會使它更快一些，但仍然很慢。 關於在哪里尋找原因的任何線索？

// create textures
glEnable(GL_TEXTURE_2D);
GLuint tex1, tex2;

// define texture properties
glGenTextures(1, &tex1);
glBindTexture(GL_TEXTURE_2D, tex1);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_BORDER_EXT);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_BORDER_EXT);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, 1280, 800, 0, GL_RGBA, GL_UNSIGNED_BYTE, 0);

// define texture properties
glGenTextures(1, &tex2);
glBindTexture(GL_TEXTURE_2D, tex2);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_BORDER_EXT);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_BORDER_EXT);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, 1280, 800, 0, GL_RGBA, GL_UNSIGNED_BYTE, 0);

// create framebuffer
GLuint fbo;
glGenFramebuffers(1, &fbo);
glBindFramebuffer(GL_FRAMEBUFFER, fbo);
glClear(GL_COLOR_BUFFER_BIT);

// create program
QGLShaderProgram program;
program.addShaderFromSourceFile(QGLShader::Fragment, ":/shaders/fshader.glsl");
program.addShaderFromSourceFile(QGLShader::Vertex, ":/shaders/vshader.glsl");
program.link();
program.bind();

//
float vertices[16];
int i = 0;
vertices[i++] = 0.0f; vertices[i++] = 0.0f; vertices[i++] = 0.0; vertices[i++] = 1.0;
vertices[i++] = 0.0f; vertices[i++] = 1280.0f; vertices[i++] = 0.0; vertices[i++] = 0.0;
vertices[i++] = 1280.0f; vertices[i++] = 0.0f; vertices[i++] = 1.0; vertices[i++] = 1.0;
vertices[i++] = 1280.0f; vertices[i++] = 1280.0f; vertices[i++] = 1.0; vertices[i++] = 0.0;
int vertexLocation = program.attributeLocation("a_position");
program.enableAttributeArray(vertexLocation);
glVertexAttribPointer(vertexLocation, 2, GL_FLOAT, GL_FALSE, 4*sizeof(float), (const void *)vertices);
int texcoordLocation = program.attributeLocation("a_texcoord");
program.enableAttributeArray(texcoordLocation);
glVertexAttribPointer(texcoordLocation, 2, GL_FLOAT, GL_FALSE, 4*sizeof(float), (const void *)(vertices + 2));

QMatrix4x4 textureMatrix, modelViewMatrix;

// do loop test
int count = 10000;
bool swapped = false;
cout << "Start fbo test" << endl;
QTime myTimer;
myTimer.start();

textureMatrix.setToIdentity();
program.setUniformValue("textureMatrix", textureMatrix);

modelViewMatrix.setToIdentity();
program.setUniformValue("modelViewProjectionMatrix", modelViewMatrix);

program.setUniformValue("srcTex", 0);

for(int i = 0; i < count; i++)
{
    glBindFramebuffer(GL_FRAMEBUFFER, fbo);
    glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0,
                              GL_TEXTURE_2D, swapped? tex2 : tex1, 0);

    // check completeness
    GLenum status;
    status = glCheckFramebufferStatus(GL_FRAMEBUFFER);
    switch(status)
    {
        case GL_FRAMEBUFFER_COMPLETE:
            break;
        default:
            log("Framebuffer error");
    }

    glEnable(GL_TEXTURE_2D);
    glBindTexture(GL_TEXTURE_2D, swapped? tex1 : tex2);

    // draw slab
    glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);

    swapped = !swapped;
}

這是頂點着色器：

#ifdef GL_ES
// Set default precision to medium
precision mediump int;
precision mediump float;
#endif

uniform mat4 modelViewProjectionMatrix;
uniform mat4 textureMatrix;

attribute vec4 a_position;
attribute vec2 a_texcoord;

varying vec2 v_texcoord;

void main()
{
    // Calculate vertex position in screen space
    gl_Position = modelViewProjectionMatrix* a_position;
    v_texcoord = vec4(textureMatrix * vec4(a_texcoord, 0.0, 1.0)).xy;
}

和片段着色器：

#ifdef GL_ES
// Set default precision to medium
precision mediump int;
precision mediump float;
#endif

uniform sampler2D srcTex;

varying vec2 v_texcoord;

void main(void)
{
    vec4 f = texture2D(srcTex, v_texcoord);
    gl_FragColor = vec4(1.0, 0.0, 0.0, 1.0);
}

Answer 1

使用兩個FBO，每個FBO都綁定到單獨的紋理，而不是在循環內交換。 調用glClear()后glBindFramebuffer()循環中，如果你不希望保留在質地的內容。