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I currently have some heat-map data in a database. I was successful in creating painting a heat-map using the same data [using some vertex shading] onto a plane. Example:
Heat-Map Image example for openGL
Name: Capture.jpg
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Now, the problem is that I am currently using something like :
glBegin(GL_QUADS);
glColor4ub(point1.color.red(), point1.color.green(), point1.color.blue(), transparency);
glVertex3d(point1.xCood - 750, point1.yCood - 750, 0);
glColor4ub(point2.color.red(), point2.color.green(), point2.color.blue(), transparency);
glVertex3d(point2.xCood - 750, point2.yCood - 750, 0);
glColor4ub(point3.color.red(), point3.color.green(), point3.color.blue(), transparency);
glVertex3d(point3.xCood - 750, point3.yCood - 750, 0);
glColor4ub(point4.color.red(), point4.color.green(), point4.color.blue(), transparency);
glVertex3d(point4.xCood - 750, point4.yCood - 750, 0);
glEnd();
And what this does [at least in my theory] is that it creates another layer over the existing plane. This causes code on clicking the plane below to be rendered useless. Changing the existing code too much is not an option right now as I do not have access to edit it. I found that if I draw a texture (rather than color a plane) on the old plane, the code stays working.
Example(texture tile just defines number of repetitions required, value is 1 in this case):
glBegin(GL_QUADS);
glTexCoord2d(0.0, textureTile);
glVertex3d(gridRect.left(), gridRect.top(), 0.0);
glTexCoord2d(0.0, 0.0);
glVertex3d(gridRect.left(), gridRect.bottom(), 0.0);
glTexCoord2d(textureTile, 0.0);
glVertex3d(gridRect.right(), gridRect.bottom(), 0.0);
glTexCoord2d(textureTile, textureTile);
glVertex3d(gridRect.right(), gridRect.top(), 0.0);
glEnd();
That said, I was only successful in loading a texture from an image I made. Since the image is suppose to be calculated and painted during run time, I tried making an image from the data to load as a texture.
I used the Qt API functionality for achieving the same. I failed to recreate the same image. Might I be suggested a way to create a texture image from data owned.
Thanks
Sorry for the late answering(in case someone else wanted the answer).
I found the answer to be the use of QOpenGLFramebufferObject.
Final code looks something like:
glViewport(0, 0, VIEW_PORT_SIZE, VIEW_PORT_SIZE);
QOpenGLFramebufferObject fbObject(VIEW_PORT_SIZE, VIEW_PORT_SIZE);
fbObject.bind();
glEnable(GL_BLEND);
glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
glPolygonMode(GL_FRONT_AND_BACK, GL_FILL);
//Switch to Ortho Mode
glMatrixMode(GL_PROJECTION); // Select Projection
glPushMatrix(); // Push The Matrix
glLoadIdentity(); // Reset The Matrix
glOrtho(left, right, bottom, top, -100, 100); // Select Ortho Mode
glMatrixMode(GL_MODELVIEW); // Select Modelview Matrix
glPushMatrix(); // Push The Matrix
glLoadIdentity(); // Reset The Matrix
//Initialize variables
SPointData point1, point2, point3, point4;
//Paint on buffer
//.................<some painting task>................
//Switch to perspective mode
glMatrixMode(GL_PROJECTION); // Select Projection
glPopMatrix(); // Pop The Matrix
glMatrixMode(GL_MODELVIEW); // Select Modelview
glPopMatrix(); // Pop The Matrix
fbObject.release();
return fbObject.toImage();
So I draw an 'I' and use gluLookAt(0.f,0.f,3.f,0.f,0.f,0.f,0.f,1.f,0.f), and the I is moderate size. Then I add a drawScene() function which draw the background with gradient color, and then the 'I' becomes super big. I guess it is because I change matrix mode to GL_PROJECTION and GL_MODELVIEW in drawScene(), and those change the perspective maybe? I guess glPushMatrix() and glPopMatrix() are needed to reserve matrix status, but I have hard time finding where to put them. So how can I make the 'I' look normal size? Here are my drawI() and drawScene():
void drawI(int format)
{
glBegin(format);
glColor3f(0, 0, 1);
glVertex2f(point[3][0], point[3][1]);
glVertex2f(point[2][0], point[2][1]);
glVertex2f(point[1][0], point[1][1]);
glVertex2f(point[12][0], point[12][1]);
glVertex2f(point[10][0], point[10][1]);
glEnd();
glBegin(format);
glVertex2f(point[10][0], point[10][1]);
glVertex2f(point[11][0], point[11][1]);
glVertex2f(point[12][0], point[12][1]);
glEnd();
glBegin(format);
glVertex2f(point[9][0], point[9][1]);
glVertex2f(point[10][0], point[10][1]);
glVertex2f(point[3][0], point[3][1]);
glVertex2f(point[4][0], point[4][1]);
glVertex2f(point[6][0], point[6][1]);
glColor3f(1, 0.5, 0);
glVertex2f(point[7][0], point[7][1]);
glVertex2f(point[8][0], point[8][1]);
glEnd();
glBegin(format);
glColor3f(0, 0, 1);
glVertex2f(point[5][0], point[5][1]);
glVertex2f(point[6][0], point[6][1]);
glVertex2f(point[4][0], point[4][1]);
glEnd();
}
void drawScene()
{
glBegin(GL_QUADS);
//red color
glColor3f(1.0,0.0,0.0);
glVertex2f(-1.0,-1.0);
glVertex2f(1.0,-1.0);
//blue color
glColor3f(0.0,0.0,1.0);
glVertex2f(1.0, 1.0);
glVertex2f(-1.0, 1.0);
glEnd();
}
Thanks a lot!
So I take glMatrixMode() and glLoadIdentity() out of drawScene() and drawI() and put them in display(). I changed drawScene() and drawI() above, and here is my display()
void display()
{
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluPerspective(70.f,1.f,0.001f,30.f);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
drawScene();
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
gluLookAt(0.f,0.f,3.f,0.f,0.f,0.f,0.f,1.f,0.f);
drawI(GL_TRIANGLE_FAN);
glutSwapBuffers();
}
The normal way to do this (in a 3D mode) is in your code, before you call drawI or drawScene would be:
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluPerspective(fov, aspect, near, far); // fov is camera angle in degrees, aspect is width/height of your viewing area, near and far are your near and far clipping planes.
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
gluLookAt(0.0,0.0,3.0,0.0,0.0,0.0,0.0,1.0,0.0)
In your 2D rendering, you probably don't need the call to gluPerspective, but these calls should be done in your code before you call drawI or drawScene. Do this and delete the glMatrixMode() and glLoadIdentity() calls from drawI and drawScene.
Edit:
If your "I" is still too big, there are a number of things you could do, but you should probably be operating in 3D (giving a Z coordinate also).
You could scale the object:
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
gluLookAt(0.0,0.0,3.0,0.0,0.0,0.0,0.0,1.0,0.0)
glScalef(0.5, 0.5, 0.5);
You could move the camera further back (you'll need to include the gluPerspective() call as well):
gluLookAt(0.0,0.0,50.0,0.0,0.0,0.0,0.0,1.0,0.0);
Perhaps the easiest way to control the rendered image size in a 3D mode is to both move the camera (eye) back a way and then control the image size by changing the camera aperture angle (fov in the gluPerspective() call). A wider fov will shrink the rendered image; a smaller fov will enlarge it.
I don't know what the values for your coordinates are in drawI since they're variables, but a camera position of 3.0, an fov of 70.0 and an aspect of 1 should give you left, right, top and bottom clipping planes of about +/- 2.1 at Z = 0.
If you kept everything else the same and moved the camera to 50.0, the clipping planes would be at about +/- 35.0, so your "I" would occupy a much smaller portion of the viewing area.
If you then left the camera position at 50.0, but changed the fov to 40.0, the clipping planes would be at about +/- 18.2. Your "I" would fill a larger area than it did at cameraZ = 50.0, fov = 70.0, but a smaller area than cameraZ = 3.0, fov = 70.0.
You can play with camera position and fov to get the image size you want, or you could just scale the image. I like to keep camera position constant and change the fov. If I provide a function that changes the fov based on user input (maybe a mouse scroll), it's a good way to provide a zoom in/out effect.
BTW, in your original code, if you called:
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
gluLookAt(0.0,0.0,3.0,0.0,0.0,0.0,0.0,1.0,0.0)
Then later in DrawI or drawScene call:
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
You've trashed the matrix loaded by your earlier call to gluLookAt().
I am having some trouble with full screen mode. I can set my window to be 800x600, but when I full screen that resolution, it stretches. I assume this is because of a change in aspect ratio. How can I fix this?
Edit #1
Here's a screen shot of what I see happening.
Left: 800x600
Right: 1366x768
Edit #2
My initGraphics function gets called every time I re-size the window (WM_SIZE).
void initGraphics(int width, int height) {
float aspect = (float)width / (float)height;
glViewport(0, 0, width, height);
glEnable(GL_TEXTURE_2D);
glEnable(GL_BLEND); //Enable alpha blending
glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
glClearColor(0.0, 0.0, 0.0, 1.0);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluOrtho2D(0.0, width, height * aspect, 0.0);
glMatrixMode(GL_MODELVIEW);
}
SOLUTION:
The real problem ended up being that you were misusing the gluOrtho2D function. Instead of using this:
gluOrtho2D(0.0, width, height * aspect, 0.0);
You needed to switch it to the correct form this:
gluOrtho2D(0.0, width, 0.0, height);
The latter creates a 2D orthographic projection, that fills the entire width and height of your viewport, so no stretching occurs.
ORIGINAL ANSWER:
You need to modify your projection in order to account for the new aspect ratio.
Make sure you first of all set glViewport to the new window size. After the viewport is set you will need to switch your matrix mode to projection with a call to glMatrixMode and then finally calculate your new aspect ratio with width / height and pass the new aspect ratio to gluPerspective. You can also use straight glFrustum instead of gluPerspective you can find source to gluPerspective to achieve that same effect with glFrustum.
Something like this:
float aspectRatio = width / height;
glMatrixMode(GL_PROJECTION_MATRIX);
glLoadIdentity();
gluPerspective(fov, aspectRatio, near, far);
After resizing the window, you need to adjust your projection matrix to reflect the new aspect ratio. If you're using classic OpenGL, switch the matrix mode to GL_PROJECTION, load the identity matrix, then call glOrtho or gluPerspective with the vertical dimension scaled by the aspect ratio (assuming you want the horizontal spread of the image to be the same as it was with the original window).
I'm wondering if it is possible to simulate the effect of looking through the keyhole in OpenGL.
I have my 3D scene drawn but I want to make everythig black everything except a central circle.
I tried this solution but its doing the completely opposite of what I want:
// here i draw my 3D scene
// Begin 2D orthographic mode
glMatrixMode(GL_PROJECTION);
glPushMatrix();
glLoadIdentity();
GLint viewport [4];
glGetIntegerv(GL_VIEWPORT, viewport);
gluOrtho2D(0, viewport[2], viewport[3], 0);
glMatrixMode(GL_MODELVIEW);
glPushMatrix();
glLoadIdentity();
// Here I draw a circle in the center of the screen
float radius=50;
glBegin(GL_TRIANGLE_FAN);
glVertex2f(x, y);
for( int n = 0; n <= 100; ++n )
{
float const t = 2*M_PI*(float)n/(float)100;
glVertex2f(x + sin(t)*r, y + cos(t)*r);
}
glEnd();
// end orthographic 2D mode
glMatrixMode(GL_PROJECTION);
glPopMatrix();
glMatrixMode(GL_MODELVIEW);
glPopMatrix();
What I get is a circle drawn in the center, but I would like to obtain its complementary...
Like everything else in OpenGL, there are a few ways to do this. Here are two off the top of my head.
Use a circle texture: (recommended)
Draw the scene.
Switch to an orthographic projection, and draw a quad over the entire screen using a texture which has a white circle at the center. Use the appropriate blending function:
glEnable(GL_BLEND);
glBlendFunc(GL_ZERO, GL_SRC_COLOR);
/* Draw a full-screen quad with a white circle at the center */
Alternatively, you can use a pixel shader to generate the circular shape.
Use a stencil test: (not recommended, but it may be easier if you don't have textures or shaders)
Clear the stencil buffer, and draw the circle into it.
glEnable(GL_STENCIL_TEST);
glStencilFunc(GL_ALWAYS, 1, 1);
glStencilOp(GL_REPLACE, GL_REPLACE, GL_REPLACE);
/* draw circle */
Enable the stencil test for the remainder of the scene.
glEnable(GL_STENCIL_TEST)
glStencilFunc(GL_EQUAL, 1, 1);
glStencileOp(GL_KEEP, GL_KEEP, GL_KEEP);
/* Draw the scene */
Footnote: I recommend avoiding use of immediate mode at any point in your code, and using arrays instead. This will improve the compatibility, maintainability, readibility, and performance of your code --- a win in all areas.
Most of this code should be fairly self explanatory. I got an display function and my view port function. There are two modes which is 4 small view ports in the window or one large.
I got one camera which can be moved and if in 4 view port mode just 3 fixed angles. The thing is I want the free moving cameras position to be displayed in the 3 other view ports. I tried doing it by drawing spheres using opengl but the problem is that then the position gets draw in the free roaming camera too as it shows the same scene.
It doesn't have to be a sphere, just something simple that represents the cameras spacial position in these three other views.
Drawing the scene once with camera object showing for the three viewports, render to texture. Clear and draw scene without camera object render to texture and then stitch these together before actually drawing the scene seems like a lot o work for something that should be easy.
void display(int what)
{
if(what==5){
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
camControll();}
if(what==1){
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
gluLookAt(75,15,-5,0,5,-5,0,1,0);}
if(what==2){
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
gluLookAt(0,110,0,0,0,0,1,0,0);}
if(what==3){
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluPerspective(45.0f, float(320) / float(240), 0.1f, 100.0f);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
camControll();}
if(what==4){
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
gluLookAt(185,75,25,0,28,0,0,1,0);}
glClearColor(0, 0, 0, 1);
glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT);
drawScene();
drawCamera();
glutSwapBuffers();
}
void viewport(){
glEnable(GL_SCISSOR_TEST);
if(!divided_view_port)
{
glViewport(0, 0, w, h);
glScissor(0,0,640,480);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluPerspective(45.0f, w / h, 0.1f, 100.0f);
display(5);
}
else
{
////////////////////// bottom left - working
glViewport(0, 0, w/2, h/2);
glScissor(0,0,w/2,h/2);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluPerspective(45.0f, w / h, 0.1f, 300.0f);
display(1);
//////////////////////
////////////////////// top right - working
glViewport(w/2, h/2, w/2, h/2);
glScissor(w/2,h/2,w/2,h/2);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluPerspective(45.0f, w / h, 0.1f, 300.0f);
display(2);
//////////////////////
////////////////////// bottom right -working
glViewport(w/2, 0, w/2, h/2);
glScissor(w/2,0,w/2,h/2);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluPerspective(45.0f, w / h, 0.1f, 300.0f);
display(3);
////////////////////////
////////////////////////// top left
glViewport(0, h/2, w/2, h/2);
glScissor(0,h/2,w/2,h/2);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluPerspective(45.0f, w / h, 0.1f, 300.0f);
display(4);
///////////////////////////
}
glDisable(GL_SCISSOR_TEST);
glMatrixMode(GL_MODELVIEW);
}
So what I basically need is to hide this object in specific viewport.
Why not make that single Sphere object (or the entity responsible for drawing the sphere) aware of the "current viewport" (which happens to be the what variable in your code) and let it be invisible if it's the given viewport?
This solution exactly corresponds to the logic involved here sounds both simple and correct.
A more general solution would be to give each "camera" a GUID and make it available for the entity responsible for drawing Cameras to check the GUID of the "camera" bound to the viewport which is being rendered at the moment. If they happen to be equal, ignore the camera object during this draw pass.
I think that should be easy if you would just draw point, because if you want to see point in viewport, its center have to be in viewport, otherwise nothing of it is displayed even if you set huge point size. Then you have 2 options to eliminate flickering effect (as when you put 2 squares in the very same possition they will flicker one over another). You can just move that point little behind camera, or use nonzero value for near clipping plane in glFrustrum/gluPerspective call.. and well if you update point position every time you move camera you have no chance of seeing that point in your moving camera and you can use single scene.
And second option, I don't know if you can update just single viewport, but maybe just setting scene, displaying it to moving camera, drawing camera position and displaying it for other 3 viewports should be easy also..
Why don't you draw the sphere behind the moving camera's near plane? That should ensure that the moving camera doesn't see the sphere at all, but its position is clearly marked for the others.