为什么是红整型¶

Red：单通道 32 INT，更多的实体容纳范围

Framebuffer¶

    enum class FramebufferTextureFormat
    {
        None = 0,
        // Color
        RGBA8, 
        //新的
        RED_INTEGER,
        // Depth/stencil
        DEPTH24STENCIL8,
        // Defaults
        Depth = DEPTH24STENCIL8
    };

        virtual int ReadPixel(uint32_t attachmentIndex, int x, int y) = 0;

OpenGL对应实现¶

主要是根据下面这个函数，取样拿到internalFormat

glTexImage2DMultisample(GL_TEXTURE_2D_MULTISAMPLE, samples, internalFormat, width, height, GL_FALSE);

代码

    static void AttachColorTexture(uint32_t id, int samples, GLenum internalFormat, GLenum format, uint32_t width, uint32_t height, int index)

        {
            bool multisampled = samples > 1;
            if (multisampled)
            {
                glTexImage2DMultisample(GL_TEXTURE_2D_MULTISAMPLE, samples, internalFormat, width, height, GL_FALSE);
            }
            else
            {
                glTexImage2D(GL_TEXTURE_2D, 0, internalFormat, width, height, 0, format, GL_UNSIGNED_BYTE, nullptr);
                glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
                glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
                glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_R, GL_CLAMP_TO_EDGE);
                glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
                glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
            }
            glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0 + index, TextureTarget(multisampled), id, 0);
        }
        static void AttachDepthTexture(uint32_t id, int samples, GLenum format, GLenum attachmentType, uint32_t width, uint32_t height)
        {
            bool multisampled = samples > 1;
            if (multisampled)
            {
                glTexImage2DMultisample(GL_TEXTURE_2D_MULTISAMPLE, samples, format, width, height, GL_FALSE);
            }
            else
            {
                glTexStorage2D(GL_TEXTURE_2D, 1, format, width, height);
                glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
                glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
                glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_R, GL_CLAMP_TO_EDGE);
                glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
                glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
            }
            glFramebufferTexture2D(GL_FRAMEBUFFER, attachmentType, TextureTarget(multisampled), id, 0);
        }

单独处理¶

                case FramebufferTextureFormat::RED_INTEGER:
                    Utils::AttachColorTexture(m_ColorAttachments[i], m_Specification.Samples, GL_R32I, GL_RED_INTEGER, m_Specification.Width, m_Specification.Height, i);

ReadPixel¶

传入坐标，读对应的缓冲区附件，然后读对应的像素点 glReadPixels(x, y, 1, 1, GL_RED_INTEGER, GL_INT, &pixelData);：这个函数调用从帧缓冲对象中读取像素数据。参数如下： - x 和 y：指定要读取的像素的坐标。 - 1 和 1：指定要读取的像素区域的宽度和高度，这里是单个像素。 - GL_RED_INTEGER：指定要读取的像素数据的格式，这里是红色通道的整型数据。 - GL_INT：指定像素数据的数据类型，这里是整型。 - &pixelData：指向存储读取数据的变量的指针。函数返回读取到的像素数据id

int OpenGLFramebuffer::ReadPixel(uint32_t attachmentIndex, int x, int y)
    {
        CORE_DEBUG_ASSERT(attachmentIndex < m_ColorAttachments.size());
        glReadBuffer(GL_COLOR_ATTACHMENT0 + attachmentIndex);
        int pixelData;
        glReadPixels(x, y, 1, 1, GL_RED_INTEGER, GL_INT, &pixelData);
        return pixelData;
    }

EditorLayer¶

设置bound

glm::vec2 m_ViewportBounds[2];

update里拿到位置，读取像素点，返回片元数据

        auto [mx, my] = ImGui::GetMousePos();
        mx -= m_ViewportBounds[0].x;
        my -= m_ViewportBounds[0].y;
        glm::vec2 viewportSize = m_ViewportBounds[1] - m_ViewportBounds[0];
        my = viewportSize.y - my;
        int mouseX = (int)mx;
        int mouseY = (int)my;
        if (mouseX >= 0 && mouseY >= 0 && mouseX < (int)viewportSize.x && mouseY < (int)viewportSize.y)
        {
            int pixelData = m_Framebuffer->ReadPixel(1, mouseX, mouseY);
            CORE_DEBUG_WARN("Pixel data = {0}", pixelData);
        }

imgui¶

update:

        //获取光标位置
        auto viewportOffset = ImGui::GetCursorPos(); // Includes tab bar

设置边界

        //设置边界
        auto windowSize = ImGui::GetWindowSize();
        ImVec2 minBound = ImGui::GetWindowPos();
        minBound.x += viewportOffset.x;
        minBound.y += viewportOffset.y;
        ImVec2 maxBound = { minBound.x + windowSize.x, minBound.y + windowSize.y };
        m_ViewportBounds[0] = { minBound.x, minBound.y };
        m_ViewportBounds[1] = { maxBound.x, maxBound.y };

GLSL¶

我们这里用color2来表示

layout(location = 0) out vec4 color;
layout(location = 1) out int color2;


void main()
{
    ...

    color2 = 50;
}

这样我们点击物体就能通过readPixel读到为50