如何将 GLSL #version 330 核心转换为 GLSL ES #version 100？

Question

我正在尝试制作一个使用 NDK 和 JNI 在 Android Studio 中绘制图像的应用程序，以使用 OpenGL ES 调用 C++ 代码。我已经阅读了如何在 OpenGL 中执行此操作的教程：https : //learnopengl.com/#!Getting-started/Textures，它使用 GLSL 330 核心。但是，Android 模拟器不支持 OpenGL ES 3.0（此链接中的注意事项：https : //developer.android.com/ndk/guides/stable_apis.html）。

因此，我必须使用 GLSL ES #version 100 ，它不支持下面着色器中的“布局”、“输入”和“输出”。我应该如何编辑它们以便它们可以在 #version 100 中运行，如果我编辑它们，源代码是否有任何变化？感谢您的关注和帮助。

更新：搜索后，我发现我可以使用 glGetAttributeLocation 来获取顶点着色器中变量的位置，而不是使用 layout(location=0)。但是，GLSL ES #version 100 中没有 VAO，所以我仍然无法弄清楚它在没有 VAO 的情况下是如何工作的。

我的顶点着色器：

#version 330 core
layout (location = 0) in vec3 position;
layout (location = 1) in vec3 color;
layout (location = 2) in vec2 texCoord;

out vec3 ourColor;
out vec2 TexCoord;

void main()
{
    gl_Position = vec4(position, 1.0f);
    ourColor = color;
    // We swap the y-axis by substracing our coordinates from 1. This is done because most images have the top y-axis inversed with OpenGL's top y-axis.
    // TexCoord = texCoord;
    TexCoord = vec2(texCoord.x, 1.0 - texCoord.y);
}

片段着色器：

#version 330 core
in vec3 ourColor;
in vec2 TexCoord;

out vec4 color;

// Texture samplers
uniform sampler2D ourTexture1;
uniform sampler2D ourTexture2;

void main()
{
    // Linearly interpolate between both textures (second texture is only slightly combined)
    color = mix(texture(ourTexture1, TexCoord), texture(ourTexture2, TexCoord), 0.2);
}

初始化 VAO,VBO,:

    // Set up vertex data (and buffer(s)) and attribute pointers
    GLfloat vertices[] = {
        // Positions          // Colors           // Texture Coords
         0.5f,  0.5f, 0.0f,   1.0f, 0.0f, 0.0f,   1.0f, 1.0f, // Top Right
         0.5f, -0.5f, 0.0f,   0.0f, 1.0f, 0.0f,   1.0f, 0.0f, // Bottom Right
        -0.5f, -0.5f, 0.0f,   0.0f, 0.0f, 1.0f,   0.0f, 0.0f, // Bottom Left
        -0.5f,  0.5f, 0.0f,   1.0f, 1.0f, 0.0f,   0.0f, 1.0f  // Top Left 
    };
    GLuint indices[] = {  // Note that we start from 0!
        0, 1, 3, // First Triangle
        1, 2, 3  // Second Triangle
    };
    GLuint VBO, VAO, ;
    glGenVertexArrays(1, &VAO);
    glGenBuffers(1, &VBO);
    glGenBuffers(1, &);

    glBindVertexArray(VAO);

    glBindBuffer(GL_ARRAY_BUFFER, VBO);
    glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);

    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, );
    glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(indices), indices, GL_STATIC_DRAW);

    // Position attribute
    glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 8 * sizeof(GLfloat), (GLvoid*)0);
    glEnableVertexAttribArray(0);
    // Color attribute
    glVertexAttribPointer(1, 3, GL_FLOAT, GL_FALSE, 8 * sizeof(GLfloat), (GLvoid*)(3 * sizeof(GLfloat)));
    glEnableVertexAttribArray(1);
    // TexCoord attribute
    glVertexAttribPointer(2, 2, GL_FLOAT, GL_FALSE, 8 * sizeof(GLfloat), (GLvoid*)(6 * sizeof(GLfloat)));
    glEnableVertexAttribArray(2);

    glBindVertexArray(0); // Unbind VAO

绘制图像：

        // Clear the colorbuffer
        glClearColor(0.2f, 0.3f, 0.3f, 1.0f);
        glClear(GL_COLOR_BUFFER_BIT);

        // Activate shader
        ourShader.Use();     

        // Bind Textures using texture units
        glActiveTexture(GL_TEXTURE0);
        glBindTexture(GL_TEXTURE_2D, texture1);
        glUniform1i(glGetUniformLocation(ourShader.Program, "ourTexture1"), 0);
        glActiveTexture(GL_TEXTURE1);
        glBindTexture(GL_TEXTURE_2D, texture2);
        glUniform1i(glGetUniformLocation(ourShader.Program, "ourTexture2"), 1);  

        // Draw container
        glBindVertexArray(VAO);
        glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, 0);
        glBindVertexArray(0);

Answer 1

最后，我设法解决了它。在 GLSL ES 100 中，没有in out和layout(location=0)我上面提到的。因此，我必须替换它们：

in => attribute

out => varying

并完全删除，layout(location=0)因为据我所知，GLSL ES 100 中没有这样的东西做同样的事情。

由于删除了layout(location=0)，我们必须告诉程序我们顶点数据的位置，在这种情况下是position，color和textCoord。使用layout(location=0)，我们可以简单地将位置 0 放在

glVertexAttribPointer(0,3, GL_FLOAT, GL_FALSE, 8 * sizeof(GLfloat), (GLvoid*)0);
glEnableVertexAttribArray(0);

没有它，我们首先需要获取顶点属性的位置：

GLint mPosition= glGetAttributeLocation(ourProgram,"position")

然后用我的预定义替换常数 0,1 或 2 mPosition：

glVertexAttribPointer(mPosition,3, GL_FLOAT, GL_FALSE, 8 * sizeof(GLfloat), (GLvoid*)0);
glEnableVertexAttribArray(mPosition);;

同样的color和textCoord。

下面是我编辑过的顶点着色器、片段着色器以及如何初始化 VBO 并传入我们的数据：

vertex shader为 GLSL ES 100编辑：

auto gVertexShader =
"attribute vec3 position;\n"
"attribute vec3 color;\n"
"attribute  vec2 texCoord;\n"

"varying vec3 ourColor;\n"
"varying vec2 TexCoord;\n"

"void main()\n"
"{\n"
    "gl_Position = vec4(position,1.0); // Add the xOffset to the x position of the vertex position\n"
    "ourColor = color;\n"
    "TexCoord= vec2(texCoord.x,1.0-texCoord.y);\n"
"}\n";

fragment shader为 GLSL ES 100编辑：

static const char FRAGMENT_SHADER[] =
    "#version 100\n"
    "precision mediump float;\n"
    "varying vec4 vColor;\n"
    "void main() {\n"
    "    gl_FragColor = vColor;\n"
    "}\n";

我的InitBuffer功能：

// Set up vertex data (and buffer(s)) and attribute pointers
    GLfloat vertices[] = {
        // Positions          // Colors           // Texture Coords
         0.5f,  0.5f, 0.0f,   1.0f, 0.0f, 0.0f,   1.0f, 1.0f, // Top Right
         0.5f, -0.5f, 0.0f,   0.0f, 1.0f, 0.0f,   1.0f, 0.0f, // Bottom Right
        -0.5f, -0.5f, 0.0f,   0.0f, 0.0f, 1.0f,   0.0f, 0.0f, // Bottom Left
        -0.5f,  0.5f, 0.0f,   1.0f, 1.0f, 0.0f,   0.0f, 1.0f  // Top Left 
    };
    GLuint indices[] = {  // Note that we start from 0!
        0, 1, 3, // First Triangle
        1, 2, 3  // Second Triangle
    };
void initBuffers()
{
    GLint mPosition,mCorlor,mTextCoord;
    GLuint VBOs[2]; // Initialize an buffer to store all the verticles and transfer them to the GPU

    glGenBuffers(2, VBOs); // Generate VBO


    glBindBuffer(GL_ARRAY_BUFFER, VBOs[0]);//Bind verticles array for OpenGL to use
    glBufferData(GL_ARRAY_BUFFER, sizeof(recVertices), recVertices, GL_STATIC_DRAW);

    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, VBOs[1]);//Bind the indices for information about drawing sequence
    glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(indices), indices, GL_STATIC_DRAW);

    // 1. set the vertex attributes pointers
    // Position Attribute
    mPosition=glGetAttributeLocation(Program, "position");
    glVertexAttribPointer(mPosition, 3, GL_FLOAT, GL_FALSE, 8 * sizeof(GLfloat), (GLvoid*)0);
    glEnableVertexAttribArray(mPosition);
    // Color Attribute

    mColor=glGetAttributeLocation(Program, "color");
    glVertexAttribPointer(mColor, 3, GL_FLOAT, GL_FALSE, 8 * sizeof(GLfloat), (GLvoid*)(3 * sizeof(GLfloat)));
    glEnableVertexAttribArray(mColor);
    //Texture Coordinate Attribute

    mTextCoord=glGetAttributeLocation(Program, "textCoord")'
    glVertexAttribPointer(mTextCoord, 2, GL_FLOAT, GL_FALSE, 8 * sizeof(GLfloat), (GLvoid*)(6 * sizeof(GLfloat)));
    glEnableVertexAttribArray(mTextCoord);


}

然后我们替换VAO在我们的抽奖函数的调用绑定initBuffer()功能

    // Clear the colorbuffer
    glClearColor(0.2f, 0.3f, 0.3f, 1.0f);
    glClear(GL_COLOR_BUFFER_BIT);

    // Activate shader
    ourShader.Use();     

    // Bind Textures using texture units
    glActiveTexture(GL_TEXTURE0);
    glBindTexture(GL_TEXTURE_2D, texture1);
    glUniform1i(glGetUniformLocation(ourShader.Program, "ourTexture1"), 0);
    glActiveTexture(GL_TEXTURE1);
    glBindTexture(GL_TEXTURE_2D, texture2);
    glUniform1i(glGetUniformLocation(ourShader.Program, "ourTexture2"), 1);  

    // Draw container
    initBuffers();
    glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, 0);
    glBindVertexArray(0);

希望这对与我有同样问题的人有所帮助。如果您有任何问题，请随时问我:)。