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beloni

OpenGL move through an image

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Hello, I need move the screen window through an large image.bmp:
//pixmap.h
typedef char byte;
typedef unsigned char ubyte;

struct pixmap
{
	unsigned width, 
					 height;
	ubyte *data;

	enum {RED = 0, GREEN, BLUE};

	pixmap(const char *fname);
	pixmap();
	~pixmap();

	void read(const char *fname);
	ubyte pixel_elem(int x, int y, int elem);
	ubyte *pixel_pos(int x, int y);
};


//pixmap.cpp

#include "pixmap.h"

#include <fstream>
#include <iostream>
#include <cstdlib>


pixmap::pixmap(const char *fname)
	: width(0), height(0), data(0)
{
	this->read(fname);
}

pixmap::pixmap()
	: width(0), height(0), data(0) {}

pixmap::~pixmap()
{
	if( data )
		delete[] data;
}

void pixmap::read(const char *fname)
{
	using namespace std;

	unsigned short planes;	// number of planes in image (must be 1) 
	unsigned short bpp;			// number of bits per pixel (must be 24)

	ifstream fin(fname, ios::in | ios::binary);
	if( !fin )
	{
		cerr << "File not found " << fname << '\n';
		exit(1);
	}
  
	fin.seekg(18, ios::cur);

	fin.read((byte *)&width, sizeof(unsigned));
	fin.read((byte *)&height, sizeof(unsigned));
	cout << "width: " << width << " height: " << height << '\n';

	fin.read((byte *)&planes, sizeof(unsigned short));
	if( planes != 1 )
	{
		cout << "Planes from " << fname << " is not 1: " << planes << "\n";
		exit(1);
	}

	fin.read((byte *)&bpp, sizeof(unsigned short));
	if( bpp != 24 )
	{
		cout << "Bpp from " << fname << " is not 24: " << bpp << "\n";
		exit(1);
	}
	
	fin.seekg(24, ios::cur);

	unsigned size(width * height * 3);				// size of the image in bytes (3 is to RGB component).
	data = new ubyte[size];
	fin.read((byte *)data, size);

	ubyte tmp;					// temporary color storage for bgr-rgb conversion.
	for( int i(0); i < size; i += 3 )
	{
		tmp = data;
		data = data[i+2];
		data[i+2] = tmp;
	}
}

ubyte pixmap::pixel_elem(int x, int y, int elem)
{
	int pos = (y*width+x) * 3 + elem;
	return data[pos];
}

ubyte *pixmap::pixel_pos(int x, int y)
{
	int pos = (y * width + x) * 3;
	return &data[pos];
}

//test program

#include <GL/glut.h>
#include <iostream>
#include <cstdlib>

#include "pixmap.h"

#define MAX_WIDTH 300
#define MAX_HEIGHT 200


pixmap *img(0);
GLfloat transx(0.0), transy(0.0);

void init_gl()
{
	glClearColor(0.0, 0.0, 0.0, 0.0);

	glMatrixMode(GL_PROJECTION);
	glLoadIdentity();
	gluOrtho2D(0.0, (GLfloat)MAX_WIDTH, 0.0, (GLfloat)MAX_HEIGHT);
}

void reshape(int w, int h)
{
	glViewport (0, 0, (GLint)w, (GLint)h);
	glMatrixMode(GL_PROJECTION);
	glLoadIdentity();
	gluOrtho2D(0.0, (GLfloat)w, 0.0, (GLfloat)h);
//	gluOrtho2D(-(GLfloat)MAX_WIDTH, (GLfloat)MAX_WIDTH, -(GLfloat)MAX_HEIGHT, (GLfloat)MAX_HEIGHT);
}

void render_scene()
{
	glClear(GL_COLOR_BUFFER_BIT);

// drawing it manually
/*	glBegin(GL_POINTS);
	for( int i(0); i < img->width; i++ )
		for( int j(0); j < img->height; j++ )
		{
//			glColor3ub(img->pixel_elem(i, j, pixmap::RED),
//								 img->pixel_elem(i, j, pixmap::GREEN),
//								 img->pixel_elem(i, j, pixmap::BLUE));
			glColor3ubv(img->pixel_pos(i, j));
			glVertex2i(i+(int)transx, j+(int)transy); 
		}
	glEnd();*/

// draw using OpenGL functions
	glTranslatef(transx, transy, 0.0);
	glRasterPos2i(0, 0);
	glDrawPixels(img->width, img->height, GL_RGB, GL_UNSIGNED_BYTE, img->data);

	glutSwapBuffers();
	glFlush();
}

void keyb_handler(unsigned char key, int x, int y)
{
	if( key == 27 )
		std::exit(0);
}

void special_key(int key, int x, int y)
{
	switch( key )
	{
		case GLUT_KEY_UP:
		{
			transy = -5.0;
			transx = 0.0;
			break;
		}

		case GLUT_KEY_DOWN:
		{
			transy = +5.0;
			transx = 0.0;
			break;
		}

		case GLUT_KEY_LEFT:
		{
			transx = +5.0;
			transy = 0.0;
			break;
		}

		case GLUT_KEY_RIGHT:
		{
			transx = -5.0;
			transy = 0.0;
			break;
		}
	}
	glutPostRedisplay();
}

void special_key2(int key, int x, int y)
{
	switch( key )
	{
		case GLUT_KEY_UP:
		{
			if( transy < MAX_HEIGHT ) transy += 5.0;
			break;
		}

		case GLUT_KEY_DOWN:
		{
			if( transy > 0 ) transy -= 5.0;
			break;
		}

		case GLUT_KEY_LEFT:
		{
			if( transx > 0 ) transx -= 5.0;
			break;
		}

		case GLUT_KEY_RIGHT:
		{
			if( transx < MAX_WIDTH ) transx += 5.0;
			break;
		}
	}
	glutPostRedisplay();
}

int main(int argc, char **argv)
{
	if( argc != 2 )
	{
		std::cerr << "INVALID ARGUMENTS\n";
		std::cerr << "You should specify the pixmap to load!\n";
		return 1;
	}

	img = new pixmap(argv[1]);

	glutInit(&argc, argv);
	glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGBA);
	glutInitWindowSize(MAX_WIDTH, MAX_HEIGHT);
	glutInitWindowPosition(0, 0);
	glutCreateWindow("A pixmap loader - by Beloni");

	init_gl();

	glutDisplayFunc(&render_scene);
	glutReshapeFunc(&reshape);
	glutKeyboardFunc(&keyb_handler);
	glutSpecialFunc(&special_key);
//	glutFullScreen();

	glutMainLoop();
	delete img;
	return 0;
}


Can you help me to do that? [Edited by - beloni on May 17, 2007 12:48:21 PM]

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You seem to have the right approach, but it's hard to see what's going wrong. Could you describe which part exactly is giving you troubles?

Also, when posting large segments of code, try to encase your code within source tags, like so (without spaces in the tags):

[ source ] _code_here_ [ /source ]

That will format your code nicely, making it easier for others to read.

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Thanks for posting source tips.
The right and up translations are done nicely, so the window actually seems to move through the image.
The problem occurs when the translation must affect the image down and left, in which image coordinates tends to zero: the image simply disappear (reasonably).
so the question is:
Quote:

How to move through an image? This like in RPG game (but this is not a game), where whatever the avatar moves, the background image (scenario) moves.


In my program, to move the image you should use the cursor keys...

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I'm not positive about this, but I'm pretty sure that using glTranslate will have no effect on glRasterPos or glDrawPixels, as those deal in window coordinates rather than 3d coordinates. One possibility would be to get rid of the glTranslate call and call glRasterPos with transx and transy instead, but I think that a better alternative would be to create a texture out of your image and then render it on a quad.

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Ok, thanks.
But how do can I create a texture of the image and render it on a quad?

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Quote:
Original post by beloni
Ok, thanks.
But how do can I create a texture of the image and render it on a quad?

NeHe has a great tutorial with sample code that shows you exactly how to do this. See the tutorial located here.

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Thanks a lot, I got it!
But it has some problems when the window is resized. Can I not allow the user resize the window in GLUT library?

That is my new source. The pixmap.h is the same as above


#include <GL/glut.h>
#include <iostream>
#include <exception>
#include <cstdlib>

#include "pixmap.h"

#define MAX_WIDTH 600
#define MAX_HEIGHT 400

pixmap *img(0);
GLfloat trans[] = {0.0, 0.0};
unsigned pos[] = {0ul, MAX_WIDTH, MAX_HEIGHT, 0ul};
GLuint texid(0);

void init_gl()
{
glClearColor(0.0, 0.0, 0.0, 0.0);

// loading texture
glGenTextures(1, &texid);
glBindTexture(GL_TEXTURE_2D, texid);

glPixelStorei(GL_UNPACK_ALIGNMENT, 1);

glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MAG_FILTER,GL_LINEAR); // scale linearly when image bigger than texture
glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MIN_FILTER,GL_LINEAR); // scale linearly when image smalled than texture

glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_MODULATE);

glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, img->width, img->height, 0, GL_RGB, GL_UNSIGNED_BYTE, img->data);

glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluOrtho2D(0.0, (GLfloat)MAX_WIDTH, 0.0, (GLfloat)MAX_HEIGHT);
}

void reshape(int w, int h)
{
glViewport (0, 0, (GLint)w, (GLint)h);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluOrtho2D(0.0, (GLfloat)w, 0.0, (GLfloat)h);
}

void render_scene()
{
glClear(GL_COLOR_BUFFER_BIT);

glEnable (GL_TEXTURE_2D); /* enable texture mapping */

glBindTexture (GL_TEXTURE_2D, texid); /* bind to our texture, has id of 13 */



glBegin(GL_QUADS);

glTexCoord2f(0.0f, 0.0f); /* lower left corner of image */

glVertex2i(0, 0);

glTexCoord2f(1.0f, 0.0f); /* lower right corner of image */

glVertex2i(img->width, 0);

glTexCoord2f(1.0f, 1.0f); /* upper right corner of image */

glVertex2i(img->width, img->height);

glTexCoord2f(0.0f, 1.0f); /* upper left corner of image */

glVertex2i(0, img->height);

glEnd ();



glDisable(GL_TEXTURE_2D); /* disable texture mapping */

glutSwapBuffers();
}

void keyb_handler(unsigned char key, int x, int y)
{
if( key == 27 )
std::exit(0);
}

void special_key(int key, int x, int y)
{
bool flag(false);
switch( key )
{
case GLUT_KEY_UP:
if( pos[2] < (img->height-1) )
{
trans[1] = -5.0;
trans[0] = 0.0;
flag = true;
pos[2] += 5;
pos[0] += 5;
}
break;

case GLUT_KEY_DOWN:
if( pos[0] > 0 )
{
trans[1] = +5.0;
trans[0] = 0.0;
flag = true;
pos[0] -= 5;
pos[2] -= 5;
}
break;

case GLUT_KEY_LEFT:
if( pos[3] > 0 )
{
trans[0] = +5.0;
trans[1] = 0.0;
flag = true;
pos[3] -= 5;
pos[1] -= 5;
}
break;

case GLUT_KEY_RIGHT:
if( pos[1] < (img->width-1) )
{
trans[0] = -5.0;
trans[1] = 0.0;
flag = true;
pos[1] += 5;
pos[3] += 5;
}
break;
}
if( flag )
{
glTranslatef(trans[0], trans[1], 0.0);
glutPostRedisplay();
}
}

int main(int argc, char **argv)
{
if( argc != 2 )
{
std::cerr << "INVALID ARGUMENTS\n";
std::cerr << "You should specify the pixmap to load!\n";
return 1;
}

try
{
img = new pixmap(argv[1]);
}
catch( std::bad_alloc &ex )
{
std::cerr << ex.what() << '\n';
return 2;
}

glutInit(&argc, argv);
glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGBA);
glutInitWindowSize(MAX_WIDTH, MAX_HEIGHT);
glutInitWindowPosition(0, 0);
glutCreateWindow("A pixmap loader - by Beloni");

init_gl();

glutDisplayFunc(&render_scene);
glutReshapeFunc(&reshape);
glutKeyboardFunc(&keyb_handler);
glutSpecialFunc(&special_key);
// glutFullScreen();

glutMainLoop();
delete img;
return 0;
}



thanks

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Quote:
Original post by beloni
Thanks a lot, I got it!
But it has some problems when the window is resized. Can I not allow the user resize the window in GLUT library?

You should be able to. What's the problem you're noticing? I haven't worked much with the GLUT library, so I'm probably not the best to answer, but if you can describe what's going on, I'm sure someone else could give some insight.

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I am so sorry...
Just not allowing the user to resize the window will solve my problem.
That is the problem: not allow the user to resize the window.

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      I generate the shadow volumes using a geometry shader with reversed extrusion (projecting the lightfacing triangles to infinity) and write the stencil buffer according to z-fail. The base of my code is the "lighting" chapter from learnopengl.com, where i extended the shader class to include geometry shader. I also modified the "lightingshader" to draw the ambient pass when "pass" is set to true and the diffuse/ specular pass when set to false. For easier testing i added a view controls to switch on/off the shadow volumes' color rendering or to change the cubes' position, i made the lightnumber controllable and changed the diffuse pass to render green for easier visualization of my problem.
       
      The first picture shows the rendered scene for one point light, all cubes and the front cube's shadow volume is the only one created (intentional). Here, all is rendered as it should be with all lit areas green and all areas inside the shadow volume black (with the volume's sides blended over).

      If i now turn on the shadow volumes for all the other cubes, we get a bit of a mess, but its also obvious that some areas that were in shadow before are now erroneously lit (for example the first cube to the right from the originaly shadow volumed cube). From my testing the areas erroneously lit are the ones where more than one shadow volume marks the area as shadowed.

      To check if a wrong stencil buffer value caused this problem i decided to change the stencil function for the diffuse pass to only render if the stencil is equal to 2. As i repeated this approach with different values for the stencil function i found out that if i set the value equal to 1 or any other uneven value the lit and shadowed areas are inverted and if i set it to 0 or any other even value i get the results shown above.
      This lead me to believe that the value and thus the stencil buffer values may be clamped to [0,1] which would also explain the artifact, because twice in shadow would equal in no shadow at all, but from what i found on the internet and from what i tested with
      GLint stencilSize = 0; glGetFramebufferAttachmentParameteriv(GL_DRAW_FRAMEBUFFER, GL_STENCIL, GL_FRAMEBUFFER_ATTACHMENT_STENCIL_SIZE, &stencilSize); my stencilsize is 8 bit, which should be values within [0,255].
      Does anyone know what might be the cause for this artifact or the confusing results with other stencil functions?
       
      // [the following code includes all used gl* functions, other parts are due to readability partialy excluded] // glfw: initialize and configure // ------------------------------ glfwInit(); glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 4); glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 4); glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE); // glfw window creation // -------------------- GLFWwindow* window = glfwCreateWindow(SCR_WIDTH, SCR_HEIGHT, "LearnOpenGL", NULL, NULL); if (window == NULL) { cout << "Failed to create GLFW window" << endl; glfwTerminate(); return -1; } glfwMakeContextCurrent(window); glfwSetFramebufferSizeCallback(window, framebuffer_size_callback); glfwSetCursorPosCallback(window, mouse_callback); glfwSetScrollCallback(window, scroll_callback); // tell GLFW to capture our mouse glfwSetInputMode(window, GLFW_CURSOR, GLFW_CURSOR_DISABLED); // glad: load all OpenGL function pointers // --------------------------------------- if (!gladLoadGLLoader((GLADloadproc)glfwGetProcAddress)) { cout << "Failed to initialize GLAD" << endl; return -1; } // ==================================================================================================== // window and functions are set up // ==================================================================================================== // configure global opengl state // ----------------------------- glEnable(GL_DEPTH_TEST); glEnable(GL_CULL_FACE); // build and compile our shader program [...] // set up vertex data (and buffer(s)) and configure vertex attributes [...] // shader configuration [...] // render loop // =========== while (!glfwWindowShouldClose(window)) { // input processing and fps calculation[...] // render // ------ glClearColor(0.1f, 0.1f, 0.1f, 1.0f); glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); glDepthMask(GL_TRUE); //enable depth writing glDepthFunc(GL_LEQUAL); //avoid z-fighting //draw ambient component into color and depth buffer view = camera.GetViewMatrix(); projection = glm::perspective(glm::radians(camera.Zoom), (float)SCR_WIDTH / (float)SCR_HEIGHT, 0.1f, 100.0f); // setting up lighting shader for ambient pass [...] // render the cubes glBindVertexArray(cubeVAO); for (unsigned int i = 0; i < 10; i++) { //position cube [...] glDrawArrays(GL_TRIANGLES, 0, 36); } //------------------------------------------------------------------------------------------------------------------------ glDepthMask(GL_FALSE); //disable depth writing glEnable(GL_BLEND); glBlendFunc(GL_ONE, GL_ONE); //additive blending glEnable(GL_STENCIL_TEST); //setting up shadowShader and lightingShader [...] for (int light = 0; light < lightsused; light++) { glDepthFunc(GL_LESS); glClear(GL_STENCIL_BUFFER_BIT); //configure stencil ops for front- and backface to write according to z-fail glStencilOpSeparate(GL_FRONT, GL_KEEP, GL_DECR_WRAP, GL_KEEP); //-1 for front-facing glStencilOpSeparate(GL_BACK, GL_KEEP, GL_INCR_WRAP, GL_KEEP); //+1 for back-facing glStencilFunc(GL_ALWAYS, 0, GL_TRUE); //stencil test always passes if(hidevolumes) glColorMask(GL_FALSE, GL_FALSE, GL_FALSE, GL_FALSE); //disable writing to the color buffer glDisable(GL_CULL_FACE); glEnable(GL_DEPTH_CLAMP); //necessary to render SVs into infinity //draw SV------------------- shadowShader.use(); shadowShader.setInt("lightnr", light); int nr; if (onecaster) nr = 1; else nr = 10; for (int i = 0; i < nr; i++) { //position cube[...] glDrawArrays(GL_TRIANGLES, 0, 36); } //-------------------------- glDisable(GL_DEPTH_CLAMP); glEnable(GL_CULL_FACE); glStencilFunc(GL_EQUAL, 0, GL_TRUE); //stencil test passes for ==0 so only for non shadowed areas glStencilOp(GL_KEEP, GL_KEEP, GL_KEEP); //keep stencil values for illumination glColorMask(GL_TRUE, GL_TRUE, GL_TRUE, GL_TRUE); //enable writing to the color buffer glDepthFunc(GL_LEQUAL); //avoid z-fighting //draw diffuse and specular pass lightingShader.use(); lightingShader.setInt("lightnr", light); // render the cubes for (unsigned int i = 0; i < 10; i++) { //position cube[...] glDrawArrays(GL_TRIANGLES, 0, 36); } } glDisable(GL_BLEND); glDepthMask(GL_TRUE); //enable depth writing glDisable(GL_STENCIL_TEST); //------------------------------------------------------------------------------------------------------------------------ // also draw the lamp object(s) [...] // glfw: swap buffers and poll IO events (keys pressed/released, mouse moved etc.) // ------------------------------------------------------------------------------- glfwSwapBuffers(window); glfwP } // optional: de-allocate all resources once they've outlived their purpose: // ------------------------------------------------------------------------ glDeleteVertexArrays(1, &cubeVAO); glDeleteVertexArrays(1, &lightVAO); glDeleteBuffers(1, &VBO); // glfw: terminate, clearing all previously allocated GLFW resources. // ------------------------------------------------------------------ glfwTerminate(); return 0;  
    • By Green_Baron
      Hi,
      i am self teaching me graphics and oo programming and came upon this:
      My Window class creates an input handler instance, the glfw user pointer is redirected to that object and methods there do the input handling for keyboard and mouse. That works. Now as part of the input handling i have an orbiting camera that is controlled by mouse movement. GLFW_CURSOR_DISABLED is set as proposed in the glfw manual. The manual says that in this case the cursor is automagically reset to the window's center. But if i don't reset it manually with glfwSetCursorPos( center ) mouse values seem to add up until the scene is locked up.
      Here are some code snippets, mostly standard from tutorials:
      // EventHandler m_eventHandler = new EventHandler( this, glm::vec3( 0.0f, 5.0f, 0.0f ), glm::vec3( 0.0f, 1.0f, 0.0f ) ); glfwSetWindowUserPointer( m_window, m_eventHandler ); m_eventHandler->setCallbacks(); Creation of the input handler during window creation. For now, the camera is part of the input handler, hence the two vectors (position, up-vector).  In future i'll take that functionally out into an own class that inherits from the event handler.
      void EventHandler::setCallbacks() { glfwSetCursorPosCallback( m_window->getWindow(), cursorPosCallback ); glfwSetKeyCallback( m_window->getWindow(), keyCallback ); glfwSetScrollCallback( m_window->getWindow(), scrollCallback ); glfwSetMouseButtonCallback( m_window->getWindow(), mouseButtonCallback ); } Set callbacks in the input handler.
      // static void EventHandler::cursorPosCallback( GLFWwindow *w, double x, double y ) { EventHandler *c = reinterpret_cast<EventHandler *>( glfwGetWindowUserPointer( w ) ); c->onMouseMove( (float)x, (float)y ); } Example for the cursor pos callback redirection to a class method.
      // virtual void EventHandler::onMouseMove( float x, float y ) { if( x != 0 || y != 0 ) { // @todo cursor should be set automatically, according to doc if( m_window->isCursorDisabled() ) glfwSetCursorPos( m_window->getWindow(), m_center.x, m_center.y ); // switch up/down because its more intuitive m_yaw += m_mouseSensitivity * ( m_center.x - x ); m_pitch += m_mouseSensitivity * ( m_center.y - y ); // to avoid locking if( m_pitch > 89.0f ) m_pitch = 89.0f; if( m_pitch < -89.0f ) m_pitch = -89.0f; // Update Front, Right and Up Vectors updateCameraVectors(); } } // onMouseMove() Mouse movement processor method. The interesting part is the manual reset of the mouse position that made the thing work ...
      // straight line distance between the camera and look at point, here (0,0,0) float distance = glm::length( m_target - m_position ); // Calculate the camera position using the distance and angles float camX = distance * -std::sin( glm::radians( m_yaw ) ) * std::cos( glm::radians( m_pitch) ); float camY = distance * -std::sin( glm::radians( m_pitch) ); float camZ = -distance * std::cos( glm::radians( m_yaw ) ) * std::cos( glm::radians( m_pitch) ); // Set the camera position and perspective vectors m_position = glm::vec3( camX, camY, camZ ); m_front = glm::vec3( 0.0, 0.0, 0.0 ) - m_position; m_up = m_worldUp; m_right = glm::normalize( glm::cross( m_front, m_worldUp ) ); glm::lookAt( m_position, m_front, m_up ); Orbiting camera vectors calculation in updateCameraVectors().
      Now, for my understanding, as the glfw manual explicitly states that if cursor is disabled then it is reset to the center, but my code only works if it is reset manually, i fear i am doing something wrong. It is not world moving (only if there is a world to render :-)), but somehow i am curious what i am missing.
       
      I am not a professional programmer, just a hobbyist, so it may well be that i got something principally wrong :-)
      And thanks for any hints and so ...
       
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