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。我目前的目标是 iPhone 模拟器上的 OpenGL ES 2.0。
我已将问题缩小到返回 vec4(0, 0, 0, 1) 的 GLSL 的 texture2D() 函数，因为如果我用任何常量颜色替换该调用，屏幕就会填充指定的颜色。创建纹理，绑定到纹理单元 0，分配其存储空间，将其 min 和 mag 过滤器设置为 NEAREST，并将 sampler2D uniform 设置为 0。
我尝试删除所有渲染到纹理代码并显式初始化其数据，我得到相同的结果，如果直接定位屏幕帧缓冲区，我得到我期望的图像，所以我相当有信心纹理的数据是都是由我尝试从中采样的时间定义的。
我已经尝试确保我的纹理在渲染时没有绑定到任何纹理单元，但这并没有什么不同。
我也尝试过 glEnable(GL_TEXTURE_2D) 但我的印象是 ES 2.0 不再重要了。无论如何它没有帮助。
我实际上是在围绕 OpenGL ES 2.0 使用我自己的瘦 C++ 包装器库，但是如果您对 OpenGL ES 2.0 非常了解，那么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我的包装库的情况下重新编写代码。我只是想知道我是否犯了一些无论如何都会跳出来的愚蠢错误。
但是，我在最后一次 drawArrays 调用我设置的所有状态变量之前添加了普通的 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。它们只是简单地包装 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);
}
你可以在这里看到我的包装器库是如何实现的：https ://github.com/jbat-es/tsgl2
编辑：
好的，我用普通的 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);
}