OpenGL - draw pixels to screen?

Question

I want to draw a 2D array of pixel data (RGB / grayscale values) on the screen as fast as possible, using OpenGL. The pixel data changes frequently.

I had hoped that

Answer 1

My solution for getting dynamically changing image data to the screen in OpenGL,

#define WIN32_LEAN_AND_MEAN

#include "wx/wx.h"
#include "wx/sizer.h"
#include "wx/glcanvas.h"
#include "BasicGLPane.h"

// include OpenGL
#ifdef __WXMAC__
#include "OpenGL/glu.h"
#include "OpenGL/gl.h"
#else
#include 
#include 
#endif
#include "ORIScanMainFrame.h"

BEGIN_EVENT_TABLE(BasicGLPane, wxGLCanvas)
EVT_MOTION(BasicGLPane::mouseMoved)
EVT_LEFT_DOWN(BasicGLPane::mouseDown)
EVT_LEFT_UP(BasicGLPane::mouseReleased)
EVT_RIGHT_DOWN(BasicGLPane::rightClick)
EVT_LEAVE_WINDOW(BasicGLPane::mouseLeftWindow)
EVT_SIZE(BasicGLPane::resized)
EVT_KEY_DOWN(BasicGLPane::keyPressed)
EVT_KEY_UP(BasicGLPane::keyReleased)
EVT_MOUSEWHEEL(BasicGLPane::mouseWheelMoved)
EVT_PAINT(BasicGLPane::render)
END_EVENT_TABLE()

// Test data for image generation.  floats range 0.0 to 1.0, in RGBRGBRGB... order.
// Array is 1024 * 3 long. Note that 32 * 32 is 1024 and is the largest image we can randomly generate.
float* randomFloatRGB;
float* randomFloatRGBGrey;

BasicGLPane::BasicGLPane(wxFrame* parent, int* args) :
    wxGLCanvas(parent, wxID_ANY, args, wxDefaultPosition, wxDefaultSize, wxFULL_REPAINT_ON_RESIZE)
{
    m_context = new wxGLContext(this);

    randomFloatRGB = new float[1024 * 3];
    randomFloatRGBGrey = new float[1024 * 3];
    // In GL images 0,0 is in the lower left corner so the draw routine does a vertical flip to get 'regular' images right side up.
    for (int i = 0; i < 1024; i++) {
        // Red
        randomFloatRGB[i * 3] = static_cast  (rand()) / static_cast  (RAND_MAX);
        // Green
        randomFloatRGB[i * 3 + 1] = static_cast  (rand()) / static_cast  (RAND_MAX);
        // Blue
        randomFloatRGB[i * 3 + 2] = static_cast  (rand()) / static_cast  (RAND_MAX);
        // Telltale 2 white pixels in 0,0 corner.
        if (i < 2) {
            randomFloatRGB[i * 3] = randomFloatRGB[i * 3 + 1] = randomFloatRGB[i * 3 + 2] = 1.0f;
        }

        randomFloatRGBGrey[i * 3] = randomFloatRGB[i * 3];
        randomFloatRGBGrey[i * 3 + 1] = randomFloatRGB[i * 3];
        randomFloatRGBGrey[i * 3 + 2] = randomFloatRGB[i * 3];
    }

    // To avoid flashing on MSW
    SetBackgroundStyle(wxBG_STYLE_CUSTOM);
}

BasicGLPane::~BasicGLPane()
{
    delete m_context;
}

void BasicGLPane::resized(wxSizeEvent& evt)
{
    //  wxGLCanvas::OnSize(evt);
    Refresh();
}

int BasicGLPane::getWidth()
{
    return GetSize().x;
}

int BasicGLPane::getHeight()
{
    return GetSize().y;
}

void BasicGLPane::render(wxPaintEvent& evt)
{
    assert(GetParent());
    assert(GetParent()->GetParent());
    ORIScanMainFrame* mf = dynamic_cast(GetParent()->GetParent());
    assert(mf);

    switch (mf->currentMainView) {
    case ORIViewSelection::ViewCamera:
        renderCamera(evt);
        break;
    case ORIViewSelection::ViewDepth:
        renderDepth(evt);
        break;
    case ORIViewSelection::ViewPointCloud:
        renderPointCloud(evt);
        break;
    case ORIViewSelection::View3DModel:
        render3DModel(evt);
        break;
    default:
        renderNone(evt);
    }
}

void BasicGLPane::renderNone(wxPaintEvent& evt) {
    if (!IsShown())
        return;
    SetCurrent(*(m_context));
    glPushAttrib(GL_ALL_ATTRIB_BITS);
    glClearColor(0.08f, 0.11f, 0.15f, 1.0f);
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    glFlush();
    SwapBuffers();
    glPopAttrib();
}

GLuint makeOpenGlTextureFromDataLuninanceFloats(int width, int height, float* f) {
    GLuint textureID;

    glEnable(GL_TEXTURE_2D);
    glGenTextures(1, &textureID);

    // "Bind" the newly created texture : all future texture functions will modify this texture
    glBindTexture(GL_TEXTURE_2D, textureID);

    // Give the image to OpenGL
    glTexImage2D(GL_TEXTURE_2D, 0, GL_FLOAT, width, height, 0, GL_FLOAT, GL_LUMINANCE, f);

    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);

    return textureID;
}

GLuint makeOpenGlTextureFromRGBInts(int width, int height, unsigned int* f) {
    GLuint textureID;


    glEnable(GL_TEXTURE_2D);
    glGenTextures(1, &textureID);

    // "Bind" the newly created texture : all future texture functions will modify this texture
    glBindTexture(GL_TEXTURE_2D, textureID);

    // Give the image to OpenGL
    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, width, height, 0, GL_RGBA, GL_UNSIGNED_INT, f);

    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);

    return textureID;
}

/// 

/// Range of each float is 0.0f to 1.0f
/// 
/// 
/// 
/// 
/// 
GLuint makeOpenGlTextureFromRGBFloats(int width, int height, float* floatRGB) {
    GLuint textureID;

    // 4.6.0 NVIDIA 457.30  (R Keene machine, 11/25/2020)
    // auto sss = glGetString(GL_VERSION);

    glGenTextures(1, &textureID);

    // "Bind" the newly created texture : all future texture functions will modify this texture
    glBindTexture(GL_TEXTURE_2D, textureID);

    // Give the image to OpenGL
    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, width, height, 0, GL_RGB, GL_FLOAT, floatRGB);

    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);

    return textureID;
}

void BasicGLPane::DrawTextureToScreenFloat(int w, int h, float* floatDataPtr, GLuint (*textureFactory)(int width, int height, float* floatRGB)) {
    if (w <= 0 || h <= 0 || floatDataPtr == NULL || w > 5000 || h > 5000) {
        assert(false);
        return;
    }

    SetCurrent(*(m_context));

    glPushAttrib(GL_ALL_ATTRIB_BITS);
    glPushMatrix();
    glPushClientAttrib(GL_CLIENT_ALL_ATTRIB_BITS);

    glClearColor(0.15f, 0.11f, 0.02f, 1.0f);
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

    glEnable(GL_TEXTURE_2D);

    glLoadIdentity();
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();

    // 4.6.0 NVIDIA 457.30  (R Keene machine, 11/25/2020)
    // auto sss = glGetString(GL_VERSION);

    float onePixelW = (float)getWidth() / (float)w;
    float onePixelH = (float)getHeight() / (float)h;
    float orthoW = w;
    float orthoH = h;
    if (onePixelH > onePixelW) {
        orthoH = h * onePixelH / onePixelW;
    }
    else {
        orthoW = w * onePixelW / onePixelH;
    }
    // We want the image at the top of the window, not the bottom if the window is too tall.
    int topOfScreen = (float)getHeight() / onePixelH;

    // If the winjdow resizes after creation you need to change the viewport.
    glViewport(0, 0, getWidth(), getHeight());
    gluOrtho2D(0.0, orthoW, (double)topOfScreen - (double)orthoH, topOfScreen);

    GLuint myTextureName = textureFactory(w, h, floatDataPtr);

    glBegin(GL_QUADS);
    {
        // This order of UV coords and verticies will do the vertical flip of the image to get the 'regular' image 0,0
        // in the top left corner.
        glTexCoord2f(0.0f, 1.0f); glVertex3f(0.0f, 0.0f, 0.0f);
        glTexCoord2f(1.0f, 1.0f); glVertex3f(0.0f + w, 0.0f, 0.0f);
        glTexCoord2f(1.0f, 0.0f); glVertex3f(0.0f + w, 0.0f + h, 0.0f);
        glTexCoord2f(0.0f, 0.0f); glVertex3f(0.0f, 0.0f + h, 0.0f);
    }
    glEnd();

    glDeleteTextures(1, &myTextureName);

    glFlush();
    SwapBuffers();


    glPopClientAttrib();
    glPopMatrix();
    glPopAttrib();
}

void BasicGLPane::DrawTextureToScreenMat(wxPaintEvent& evt, cv::Mat m, float brightness) {
    m.type();
    if (m.empty()) {
        renderNone(evt);
        return;
    }

    if (m.type() == CV_32FC1) { // Grey scale.
        DrawTextureToScreenFloat(m.cols, m.rows, (float*)m.data, makeOpenGlTextureFromDataLuninanceFloats);
    }
    if (m.type() == CV_32FC3) { // Color.
        DrawTextureToScreenFloat(m.cols, m.rows, (float*)m.data, makeOpenGlTextureFromRGBFloats);
    }
    else {
        renderNone(evt);
    }
}

void BasicGLPane::renderCamera(wxPaintEvent& evt) {
    if (!IsShown())
        return;
    DrawTextureToScreenMat(evt, ORITopControl::Instance->im_white);
}

void BasicGLPane::renderDepth(wxPaintEvent& evt) {
    if (!IsShown())
        return;
    DrawTextureToScreenMat(evt, ORITopControl::Instance->depth_map);
}

void BasicGLPane::render3DModel(wxPaintEvent& evt) {
    if (!IsShown())
        return;
    SetCurrent(*(m_context));
    glPushAttrib(GL_ALL_ATTRIB_BITS);
    glPushMatrix();

    glClearColor(0.08f, 0.11f, 0.15f, 1.0f);
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);



    glFlush();
    SwapBuffers();

    glPopMatrix();
    glPopAttrib();
}

void BasicGLPane::renderPointCloud(wxPaintEvent& evt) {
    if (!IsShown())
        return;
    boost::unique_lock lk(ORITopControl::Instance->pointCloudCacheMutex);

    SetCurrent(*(m_context));
    glPushAttrib(GL_ALL_ATTRIB_BITS);
    glPushMatrix();

    glLoadIdentity();
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();

    glViewport(0, 0, getWidth(), getHeight());

    glClearColor(0.08f, 0.11f, 0.15f, 1.0f);
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

    if (ORITopControl::Instance->pointCloudCache.size() > 0) {
        glMatrixMode(GL_PROJECTION);
        gluPerspective( /* field of view in degree */ 40.0,
            /* aspect ratio */ 1.0,
            /* Z near */ 1.0, /* Z far */ 500.0);
        glMatrixMode(GL_MODELVIEW);
        gluLookAt(100, 70, 200, // Eye
            25, 25, 25, // Look at pt
            0, 0, 1); // Up Vector

        glPointSize(2.0);
        glBegin(GL_POINTS);
        // Use explicit for loop because pointCloudFragments can grow asynchronously.
        for (int i = 0; i < ORITopControl::Instance->pointCloudCache.size(); i++) {
            auto frag = ORITopControl::Instance->pointCloudCache[i];
            auto current_point_cloud_ptr = frag->cloud;
            glPushMatrix();
            // glMultMatrixf(frag->xform.data());
            for (size_t n = 0; n < current_point_cloud_ptr->size(); n++) {
                glColor3ub(255, 255, 255);
                glVertex3d(current_point_cloud_ptr->points[n].x, current_point_cloud_ptr->points[n].y, current_point_cloud_ptr->points[n].z);
            }
            glPopMatrix();
        }
        glEnd();
    }

    glFlush();
    SwapBuffers();

    glPopMatrix();
    glPopAttrib();
}