Question

如果在片段着色器中指定了颜色，则我的第一个三角形效果很好。当我向缓冲区添加顶点颜色时，三角形始终为黑色。

出现问题的最小代码：

type 
    OGLfloat = float32
    OGLuint = uint32
    OGLint = int32

const
    GLFW_CONTEXT_VERSION_MAJOR = 0x00022002
    GLFW_CONTEXT_VERSION_MINOR = 0x00022003
    GLFW_OPENGL_PROFILE = 0x00022008
    GLFW_OPENGL_CORE_PROFILE = 0x00032001

const 
    GL_COLOR_BUFFER_BIT = 0x00004000
    GL_DEPTH_BUFFER_BIT = 0x00000100
    GL_ACCUM_BUFFER_BIT = 0x00000200
    GL_STENCIL_BUFFER_BIT = 0x00000400
    GL_ARRAY_BUFFER = 0x8892
    GL_ELEMENT_ARRAY_BUFFER = 0x8893
    GL_FALSE = 0.char
    GL_STATIC_DRAW = 0x88E4
    GL_FLOAT = 0x1406
    GL_VERTEX_SHADER = 0x8B31
    GL_COMPILE_STATUS = 0x8B81
    GL_INFO_LOG_LENGTH = 0x8B84
    GL_FRAGMENT_SHADER = 0x8B30
    GL_LINK_STATUS = 0x8B82
    GL_TRIANGLES = 0x0004
    GL_UNSIGNED_INT= 0x1405
    GL_VERSION = 0x1F02

const 
    POSITION_LENGTH = 3
    COLOR_LENGTH = 3

const
    WINDOW_W = 640
    WINDOW_H = 480

var
    colorDataOffset = 3 * sizeof(OGLfloat)

    vertices = @[OGLfloat(0.0), 0.5, 0, 1, 1, 1,
                         0.5, -0.5, 0,  0, 0, 0,
                         -0.5, -0.5, 0,  0, 0, 0]

    indices = @[OGLuint(0), 1 , 2]

# initialisation using glfw and glew
var glfwErr = glfwInit()
glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3)
glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3)
glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE)
var winHandle = glfwCreateWindow(WINDOW_W, WINDOW_H)
glfwMakeContextCurrent(winHandle)
var glewErr = glewInit()

# shaders sources
var 
    shadID:OGLuint
    vertSrc:cstring = """
        #version 330 core
        layout (location = 0) in vec3 aPos;
        layout (location = 1) in vec3 aColor;

        out vec3 inColor;

        void main()
        {
            gl_Position = vec4(aPos, 1.0f);
            inColor = aColor;

        }
        """
    fragSrc:cstring = """
        #version 330 core
        out vec4 FragColor;        
        in vec3 inColor;

        void main()
        {
            FragColor = vec4(inColor, 1.0f);
        }

        """
# create the shader program
proc send_src(vert:var cstring, frag:var cstring):OGLuint =
    var success:OGLint
    # vertex
    var vertexShader = glCreateShader(GL_VERTEX_SHADER)
    glShaderSource(vertexShader, 1, addr vert, nil)
    glCompileShader(vertexShader)
    # Check compilation errors.
    glGetShaderiv(vertexShader, GL_COMPILE_STATUS, addr success)
    if bool(success) == false:
        echo(" vertex shader compilation failed (send_src)")
    else:
        echo("vertexShader compiled (send_src)")

    # fragment
    var fragmentShader = glCreateShader(GL_FRAGMENT_SHADER)
    glShaderSource(fragmentShader, 1, addr frag, nil)
    glCompileShader(fragmentShader)
    # Check compilation errors.
    glGetShaderiv(fragmentShader, GL_COMPILE_STATUS, addr success)
    if bool(success) == false:
        echo("fragment shader compilation failed (send_src)"
    else:
        echo("fragmentShader compiled (send_src)")

    # Shader program
    result = glCreateProgram()
    glAttachShader(result, vertexShader)
    glAttachShader(result, fragmentShader)
    glLinkProgram(result)
    # Check for linkage errors.
    glGetProgramiv(result, GL_LINK_STATUS, addr success)
    if success == 0:
        echo ("program linking failed (send_src)")
    else:
        echo ("shader linked (send_src)")

    glDeleteShader(vertexShader)
    glDeleteShader(fragmentShader)


glViewport(0, 0, WINDOW_W, WINDOW_H)
shadID = send_src(vertSrc, fragSrc)

var VAO, VBO, EBO:OGLuint
glGenVertexArrays(1, addr VAO)
glGenBuffers(1, addr VBO)
glGenBuffers(1, addr EBO)
glBindVertexArray(VAO)
glBindBuffer(GL_ARRAY_BUFFER, VBO)
glBufferData(GL_ARRAY_BUFFER, vertices.len * sizeof(OGLfloat), 
             addr vertices[0], GL_STATIC_DRAW)
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, EBO)
glBufferData(GL_ELEMENT_ARRAY_BUFFER, indices.len * sizeof(OGLuint), 
             addr indices[0], GL_STATIC_DRAW)
# Position layout
glVertexAttribPointer(0, POSITION_LENGTH, GL_FLOAT, GL_FALSE, 6 * sizeof(OGLfloat), 
                      nil)
glEnableVertexAttribArray(0)
# Color layout
glVertexAttribPointer(1, COLOR_LENGTH, GL_FLOAT, GL_FALSE, 6 * sizeof(OGLfloat), 
                      addr colorDataOffset)
glEnableVertexAttribArray(1)
glBindBuffer(GL_ARRAY_BUFFER, 0)
glBindVertexArray(0)
glUseProgram(shadID)

while bool(glfwWindowShouldClose(winHandle)) == false:
    glClearColor(0.2, 0.3, 0.3, 1.0)
    glClear(GL_COLOR_BUFFER_BIT)
    glBindVertexArray(VAO)
    glDrawElements(GL_TRIANGLES, OGLint(indices.len), GL_UNSIGNED_INT, nil)
    glfwSwapBuffers(winHandle)
    glfwPollEvents()

glDeleteVertexArrays(1, addr VAO)
glDeleteBuffers(1, addr VBO)
glDeleteBuffers(1, addr EBO)
glfwDestroyWindow(winHandle)
glfwTerminate()

Answer 1

首先见OpenGL 4.6 API Compatibility Profile Specification; 10.3.9 Vertex Arrays in Buffer Objects; page 409

...当数组从顶点属性的缓冲区对象中获取时，顶点缓冲区的偏移量设置被用作基本机器单位中的偏移量。 / strong>该缓冲区数据存储区中第一个元素。

这意味着glVertexAttribPointer的第六个参数必须是color属性的偏移量，编码为pointer。

当您在{p>中执行addr colorDataOffset时
glVertexAttribPointer(1, COLOR_LENGTH, GL_FLOAT, GL_FALSE, 6 * sizeof(OGLfloat), addr colorDataOffset)

然后创建一个pointer，但是指针的值是colorDataOffset的地址-请参见The addr operator。

您要做的是用colorDataOffset cast cast[pointer](colorDataOffset)到指针类型，指针的值必须是colorDataOffset的值-参见Type casts和Types：

glVertexAttribPointer(1, COLOR_LENGTH, GL_FLOAT, GL_FALSE, 6 * sizeof(OGLfloat), cast[pointer](colorDataOffset))

OpenGL顶点颜色总是导致黑色三角形

1 个答案: