opengl-es - GLSL texture2D() 总是返回 (0, 0, 0, 1)

Question

我对此感到非常困惑。我正在尝试渲染到屏幕外纹理，以便我可以执行一些后期处理，但甚至无法让该纹理未经修改地绘制到屏幕上。我目前在 iPhone 模拟器上以 OpenGL ES 2.0 为目标。

我已经将问题缩小到 GLSL 的 texture2D() 函数返回 vec4(0, 0, 0, 1) 因为，如果我用任何常量颜色替换该调用，屏幕将填充指定的颜色。纹理被创建，绑定(bind)到纹理单元 0，它的存储被分配，它的 min 和 mag 过滤器设置为 NEAREST，sampler2D uniform 设置为 0。

我已经尝试删除所有渲染到纹理代码并显式初始化其数据，我得到了相同的结果，如果直接将屏幕帧缓冲区作为目标，我会得到我期望的图像，所以我相当有信心纹理的数据都是在我尝试从中采样时定义的。

我已经尝试确保我的纹理在渲染时没有绑定(bind)到任何纹理单元，但这并没有什么不同。

我也试过 glEnable(GL_TEXTURE_2D) 但我的印象是它对 ES 2.0 不再重要了。无论如何它都没有帮助。

我实际上是在 OpenGL ES 2.0 周围使用我自己的精简 C++ 包装器库，但如果您非常了解 OpenGL ES 2.0，无论如何都应该清楚这段代码中发生的事情。对于代码不是普通的 OpenGL，我深表歉意；我的下一个调试步骤是在没有包装器库的情况下重写代码。我只是想知道我是否犯了任何无论如何都会跳出来的愚蠢错误。

但是，我在最后一个 drawArrays 调用我设置的所有状态变量之前添加了纯 OpenGL glGet*() 查询，并且一切都按预期设置。

代码中唯一不太明显的部分是 Smart<> 对象。它们只是包装 GL 对象引用和引用数组，并在它们的析构函数中调用它们关联的 glDelete*()。

#include <tsvl/vec.hpp>
using namespace tsvl;

#include <tsgl2/Context.hpp>
#include <tsgl2/Smart.hpp>
using namespace tsgl2;

#include <array>
#include <exception>
#include <string>
using namespace std;

#define SHADER_SOURCE(text) "#version 100\n" #text


namespace {

const AttributeLocation vertexPositionAttributeLocation(0);

const string vec2PassthroughVertexShaderSource = SHADER_SOURCE(
  attribute vec2 vertexPosition;
  void main() {
    gl_Position = vec4(vertexPosition, 0, 1);
  }
);

const string greenFragmentShaderSource = SHADER_SOURCE(
  void main() {
    gl_FragColor = vec4(0, 1, 0, 1);
  }
);

const string combineTexturesFragmentShaderSource = SHADER_SOURCE(
  precision highp float;

  uniform vec2 screenSize;
  uniform sampler2D samplers[1];

  void main() {
    vec2 texCoord = gl_FragCoord.xy / screenSize;
    gl_FragColor = texture2D(samplers[0], texCoord);
  }
);

const vec2 vertices[] = {
  vec2(-0.9f, -0.9f),
  vec2( 0.9f, -0.9f),
  vec2( 0.0f,  0.9f),
};
const int vertexCount = sizeof(vertices) / sizeof(vertices[0]);

const vec2 screenCorners[] = {
  vec2(-1.0f, -1.0f),
  vec2( 1.0f, -1.0f),
  vec2( 1.0f,  1.0f),
  vec2(-1.0f,  1.0f),
};
const int screenCornerCount = sizeof(screenCorners) / sizeof(screenCorners[0]);

} // unnamed namespace


void drawDemoScene(int screenWidth, int screenHeight) {
  FramebufferRef screenFramebuffer = Framebuffer::currentBinding();

  //

  Smart<array<TextureRef, 8>> renderTextures(Context::genTextures<8>());
  Smart<array<FramebufferRef, 8>> renderFramebuffers(Context::genFramebuffers<8>());

  Context::setActiveTextureUnit(TextureUnit(0)); // My wrapper translates this to GL_TEXTURE0
  Texture2D::bind(renderTextures.get()[0]);
  Texture2D::setStorage(TextureFormat::RGBA8, IntRect::Size(screenWidth, screenHeight));
  Texture2D::setMinificationFilter(TextureMinificationFilter::NEAREST);
  Texture2D::setMagnificationFilter(TextureMagnificationFilter::NEAREST);

  Framebuffer::bind(renderFramebuffers.get()[0]);
  Framebuffer::ColorAttachment::set(renderTextures.get()[0], FramebufferTextureTarget::TEXTURE_2D);
  if (Framebuffer::status() != FramebufferStatus::COMPLETE)
    throw exception();

  //

  vertexPositionAttributeLocation.enableAttributeArray();

  Smart<ShaderRef> vec2PassthroughVertexShader(Context::createShader(ShaderType::VERTEX));
  vec2PassthroughVertexShader->setSource(vec2PassthroughVertexShaderSource);
  vec2PassthroughVertexShader->compile();
  if (!vec2PassthroughVertexShader->compileWasSuccessful())
    throw exception();

  Smart<ShaderRef> greenFragmentShader(Context::createShader(ShaderType::FRAGMENT));
  greenFragmentShader->setSource(greenFragmentShaderSource);
  greenFragmentShader->compile();
  if (!greenFragmentShader->compileWasSuccessful())
    throw exception();

  Smart<ShaderRef> combineTexturesFragmentShader(Context::createShader(ShaderType::FRAGMENT));
  combineTexturesFragmentShader->setSource(combineTexturesFragmentShaderSource);
  combineTexturesFragmentShader->compile();
  if (!combineTexturesFragmentShader->compileWasSuccessful())
    throw exception();

  Smart<ProgramRef> vec2PassthroughGreenProgram(Context::createProgram());
  vec2PassthroughGreenProgram->attach(*vec2PassthroughVertexShader);
  vec2PassthroughGreenProgram->attach(*greenFragmentShader);
  vec2PassthroughGreenProgram->bindAttributeToLocation(
      "vertexPosition", vertexPositionAttributeLocation);
  vec2PassthroughGreenProgram->link();
  vec2PassthroughGreenProgram->validate();
  if (!vec2PassthroughGreenProgram->validationWasSuccessful())
    throw exception();

  Smart<ProgramRef> combineTexturesProgram(Context::createProgram());
  combineTexturesProgram->attach(*vec2PassthroughVertexShader);
  combineTexturesProgram->attach(*combineTexturesFragmentShader);
  combineTexturesProgram->bindAttributeToLocation(
      "vertexPosition", vertexPositionAttributeLocation);
  combineTexturesProgram->link();
  combineTexturesProgram->validate();
  if (!combineTexturesProgram->validationWasSuccessful())
    throw exception();

  UniformLocation screenSizeUniformLocation =
      combineTexturesProgram->locationOfUniform("screenSize");
  UniformLocation samplersUniformLocation =
      combineTexturesProgram->locationOfUniform("samplers");

  //

  Context::setColorClearValue(0.0f, 0.0f, 0.0f, 0.0f);
  Context::setLineWidth(2.0f);
  Context::setViewport(IntRect(0, 0, screenWidth, screenHeight));
  Context::useProgram(*vec2PassthroughGreenProgram);

  Framebuffer::bind(renderFramebuffers.get()[0]);

  vertexPositionAttributeLocation.setAttributeArrayPointerAndStride(
      DONT_NORMALIZE, 2, AttributeLocation::ArrayDataType::FLOAT, vertices, 0);

  Context::clear(CLEAR_COLOR_BUFFER);
  Context::drawArrays(DrawMode::LINE_LOOP, 0, vertexCount);

  //

  Context::enableBlending();
  Context::setBlendFuncs(SourceBlendFunc::SRC_ALPHA, DestBlendFunc::ONE_MINUS_SRC_ALPHA);
  Context::setColorClearValue(1.0f, 1.0f, 1.0f, 1.0f);
  Context::setViewport(IntRect(0, 0, screenWidth, screenHeight));
  Context::useProgram(*combineTexturesProgram);

  Framebuffer::bind(screenFramebuffer);

  vertexPositionAttributeLocation.setAttributeArrayPointerAndStride(
      DONT_NORMALIZE, 2, AttributeLocation::ArrayDataType::FLOAT, screenCorners, 0);

  screenSizeUniformLocation.setUniformValue(vec2(screenWidth, screenHeight));
  samplersUniformLocation.setUniformValue(TextureUnit(0)); // Even though setActiveTextureUnit()
                                                           // translated this to GL_TEXTURE0
                                                           // It stays plain int 0 here.

  Context::clear(CLEAR_COLOR_BUFFER);
  Context::drawArrays(DrawMode::TRIANGLE_FAN, 0, screenCornerCount);
}

您可以在此处查看我的包装器库是如何实现的:https://github.com/jbat-es/tsgl2

编辑:

好吧，我用普通 OpenGL 写了一个非常精简的版本，它有同样的问题:

void drawDemoScenePlainGL(int screenWidth, int screenHeight) {
  GLuint texture;
  glGenTextures(1, &texture);

  glBindTexture(GL_TEXTURE_2D, texture);
  int data[320][460];
  memset(data, 0xFF, 320*460*sizeof(int));
  glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, screenWidth, screenHeight, 0, GL_RGBA, GL_UNSIGNED_BYTE, data);
  glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
  glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
  glBindTexture(GL_TEXTURE_2D, 0);

  //

  glEnableVertexAttribArray(0);

  GLuint vertexShader = glCreateShader(GL_VERTEX_SHADER);
  const char* source = vec2PassthroughVertexShaderSource.c_str();
  int sourceLength = vec2PassthroughVertexShaderSource.length();
  glShaderSource(vertexShader, 1, &source, &sourceLength);
  glCompileShader(vertexShader);

  GLuint fragmentShader = glCreateShader(GL_FRAGMENT_SHADER);
  source = combineTexturesFragmentShaderSource.c_str();
  sourceLength = combineTexturesFragmentShaderSource.length();
  glShaderSource(fragmentShader, 1, &source, &sourceLength);
  glCompileShader(fragmentShader);

  GLuint program = glCreateProgram();
  glAttachShader(program, vertexShader);
  glAttachShader(program, fragmentShader);
  glBindAttribLocation(program, 0, "vertexPosition");
  glLinkProgram(program);

  GLuint screenSizeUniformLocation = glGetUniformLocation(program, "screenSize");
  GLuint samplersUniformLocation = glGetUniformLocation(program, "samplers");

  //

  glClearColor(1, 1, 1, 1);
  glUseProgram(program);
  glVertexAttribPointer(0, 2, GL_FLOAT, GL_FALSE, 0, screenCorners);
  glViewport(0, 0, screenWidth, screenHeight);

  glActiveTexture(GL_TEXTURE0);
  glBindTexture(GL_TEXTURE_2D, texture);

  glUniform2f(screenSizeUniformLocation, screenWidth, screenHeight);
  glUniform1i(samplersUniformLocation, 0);

  glClear(GL_COLOR_BUFFER_BIT);
  glDrawArrays(GL_TRIANGLE_FAN, 0, screenCornerCount);
}

Answer 1

纹理环绕模式默认为 GL_REPEAT，它只支持二次方纹理。简单地添加

glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);

解决问题。