Question

我想通过以下三种方法实现颜色选择/选择：

void ColorIndex(uint colorIndex)
{
    glColor4ubv((GLubyte *)&colorIndex);
}

void ColorIndices(vector<uint> &colorIndices)
{
    GLubyte *colorPtr = (GLubyte *)&colorIndices[0];
    glColorPointer(4, GL_UNSIGNED_BYTE, 0, colorPtr);
}

void ReadSelectedIndices(int x, int y, int width, int height, uint *selectedIndices)
{
    glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
    glReadPixels(x, y, width, height, GL_RGBA, GL_UNSIGNED_BYTE, selectedIndices);
}

它们基本上将无符号整数（32位）打包成4个字节R，G，B，A。与GL_SELECT相比，它简单而快速。

问题是它有时不起作用。在带有NVIDIA 9800显卡的Windows上，它不适用于我。它适用于Mac / Windows上的ATI Radeon 4670。

我认为问题出在alpha通道中，所以我尝试了这个实现：

union RgbColor
{
    GLuint colorIndex : 24;
    GLubyte components[3];
    struct
    {
        GLubyte r;
        GLubyte g;
        GLubyte b;
    };
};

void ColorIndex(uint colorIndex)
{
    RgbColor color;
    color.colorIndex = colorIndex;
    glColor3ubv(color.components);
}

vector<GLubyte> colorComponents;

void ColorIndices(vector<uint> &colorIndices)
{
    colorComponents.clear();

    for (uint i = 0; i < colorIndices.size(); i++)
    {
        RgbColor color;
        color.colorIndex = colorIndices[i];

        colorComponents.push_back(color.components[0]);
        colorComponents.push_back(color.components[1]);
        colorComponents.push_back(color.components[2]);
    }

    GLubyte *colorPtr = (GLubyte *)&colorComponents[0];
    glColorPointer(3, GL_UNSIGNED_BYTE, 0, colorPtr);
}

const uint kMaxSelectedIndicesCount = 2000 * 2000;  // max width * max height resolution

GLubyte colorBuffer[kMaxSelectedIndicesCount * 3];

void ReadSelectedIndices(int x, int y, int width, int height, uint *selectedIndices)
{
    uint count = (uint)width * (uint)height;

    memset(colorBuffer, 0, count * 3);

    glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
    glReadPixels(x, y, width, height, GL_RGB, GL_UNSIGNED_BYTE, colorBuffer);
    GetGLError();

    for (uint i = 0; i < count; i++)
    {
        RgbColor color;
        color.components[0] = colorBuffer[i * 3 + 0];
        color.components[1] = colorBuffer[i * 3 + 1];
        color.components[2] = colorBuffer[i * 3 + 2];

        selectedIndices[i] = color.colorIndex;
    }
}

现在，在显卡和操作系统选择都有效，但有时会选择坏顶点（在选择矩形之外）。

这怎么可能发生？有没有更好的方法来实现颜色选择，这种方法在各种图形卡上都很强大并且总是正确的？

OpenGL颜色选择RGBA与RGB

0 个答案: