I'm pretty new to OpenGL. I was playing around with some code but I can't figure out why the following will not produce two viewports with the same object view. Here's the code:
glViewport(0, windowHeight/2, windowWidth/2, windowHeight);
glScissor(0, windowHeight/2, windowWidth/2, windowHeight);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluPerspective( 45.0, (GLfloat)(windowWidth/2)/(GLfloat)(windowHeight/2), 0.1f,
500.0 );
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
glClear(GL_DEPTH_BUFFER_BIT | GL_COLOR_BUFFER_BIT);
drawParticleView();
glViewport(windowWidth/2, 0, windowWidth, windowHeight/2);
glScissor(windowWidth/2, 0, windowWidth, windowHeight/2);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluPerspective( 45.0, (GLfloat)(windowWidth/2)/(GLfloat)(windowHeight/2), 0.1f,
500.0 );
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
glClear(GL_DEPTH_BUFFER_BIT | GL_COLOR_BUFFER_BIT);
drawParticleView();
drawParticleView() just draws an array of rectangles. The problem is that the second viewport is a squashed representation of the first. My window width is 1280 and height 960. I'm obviously doing something wrong but what? Thanks
The parameters to glViewport are the lower left corner of your viewport as x and y, then width and height.
For a window of 100 pixels square, your two viewports are specified as:
x1 = 0, y1 = 50, width1 = 50, height1 = 100.
x2 = 50, y2 = 0, width2 = 100, height2 = 50.
These placements and sizes put the first viewport in the upper left quadrant of your window, hanging half out the top of your window, and the second in the lower left quadrant of your window, hanging half out the side of your window.
For side by side viewports I think you want:
glViewport(0, 0, windowWidth/2, windowHeight);
// drawing code
glViewport(windowWidth/2, 0, windowWidth/2, windowHeight);
// repeat drawing code
Or top and bottom viewports I think you want:
glViewport(0, 0, windowWidth, windowHeight/2);
// drawing code
glViewport(0, windowHeight/2, windowWidth, windowHeight/2);
// repeat drawing code
The reason your second viewport is squashed is because it's aspect ratio is inverted, and therefore the parameter to gluPerspective is wrong. The aspect ratio parameter should be (windowWidth/2)/windowHeight for the first option above, and windowWidth/(windowHeigh/2) in the second option above.
Related
I tried to draw a teapot and view it in 3D but when I ran the program, nothing showed up. There is nothing in the window. I know it has something to do with my gluLookAt() function but I am not sure how to fix it.
// helloteapot.cc
//#include <GLUT/gl.h>
#include <GLUT/glut.h>
#include "GL/glui.h"
void display () {
/* clear window */
glClear(GL_COLOR_BUFFER_BIT);
/* draw scene */
glColor3f(1.0, 0.0, 0.0);
glTranslatef(0.0, 0.5, 0.0);
glutSolidTeapot(0.15);
/* flush drawing routines to the window */
glFlush();
}
int main ( int argc, char * argv[] ) {
glutInit(&argc,argv);
/* setup the size, position, and display mode for new windows */
glutInitWindowSize(800,600);
glutInitWindowPosition(0,0);
glutInitDisplayMode(GLUT_RGB);
/* create and set up a window */
glutCreateWindow("hello, teapot!");
glutDisplayFunc(display);
/*GLfloat width = 800;
GLfloat height = 600;
GLfloat aspect = (GLfloat)width / (GLfloat)height;
// Set the viewport to cover the new window
glViewport(0, 0, width, height);*/
// Set the aspect ratio of the clipping volume to match the
viewport
glMatrixMode(GL_PROJECTION); // To operate on the Projection
matrix
glLoadIdentity(); // Reset
// Enable perspective projection with fovy, aspect, zNear and zFar
//luPerspective(45.0f, aspect, -100.0f, 100.0f);
gluLookAt(0, 0, 0, 0, 0.5, 0, 0, -1, 0);
/* tell GLUT to wait for events */
glutMainLoop();
}
You have asked GL to position the camera at the origin, aim the camera upwards towards the point (0, 0.5, 0), and have also specified (incorrectly) the up vector to be 0, -1, 0. The problem is that the camera's forward direction is (0, 1, 0) [as specified by your eye and aim positions], and this direction conflicts with the up vector or (0, -1, 0). Try using a vector at right angles to the forward direction instead! (e.g. [1, 0, 0], [0, 0, 1])
gluLookAt(
0, 0, 0, //< camera location
0, 0.5, 0, //< looking towards point
1, 0, 0); //< which direction is up?
I am trying to setup my OpenGL views for some texture rendering. Following some advice on the forum, I set up my viewport and ortho matrix as follows:
First I try to compute the screen width and height that I can use while maintaining the aspect ratio of my image:
void resize(int w, int h)
{
float target_aspect_ratio = image_width / image_height;
width = w;
height = (int)(width / target_aspect_ratio + 0.5f);
if (height > h) {
height = h;
width = (int)(height * target_aspect_ratio + 0.5f);
}
off_x = (w - width)/2.f;
off_y = (h - height)/2;
// I want to center my image. So I have these offsets
glViewport(off_x, off_y, width, height);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glOrtho(0, width, 0, height, 0.0f, 1.0f);
Now when I want to render my texture I do:
void paint()
{
// texture binding etc.
glTexCoord2f(0, 0); glVertex2f(0, 0);
glTexCoord2f(1, 0); glVertex2f(width, 0);
glTexCoord2f(1, 1); glVertex2f(width, height);
glTexCoord2f(0, 1); glVertex2f(0, height);
}
However, this does not show the image as expected. It does not maintain the aspect ratio as I size the screen. It is almost like the glViewport has no effect and I can verify this function gets called every time my window is resized.
Update:
It is strange. Almost as if these calls have no effect. I even did something as:
_off_x = _off_y = 0;
_width = 500;
_height = 500;
So I expected the viewport to be lower left box of my screen but the image is being drawn as before basically using the whole screen as the viewport.
Update 2:
Ok, so if I call
glViewport(_off_x, _off_y, _width, _height);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glOrtho(0, _width, 0, _height, 0, 1);
in my paint events, it works as expected! However, I thought it was enough to put this in the resize event handler.
Before start drawing, you need to switch your Matrix mode to GL_MODELVIEW. You don't need to set your projection matrix inside your render function at each frame.
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
Here is a detailed analysis that I wrote about glMatrixMode() function modes :
OpenGL glMatrixMode(GL_PROJECTION) vs glMatrixMode(GL_MODELVIEW)
When my window is resized, i don't want the contents to scale but just to increase the view port size. I found this while searching on stackoverflow (http://stackoverflow.com/questions/5894866/resize-viewport-crop-scene) which is pretty much the same as my problem. However I'm confused as to what to set the Zoom to and where, i tried it with 1.0f but then nothing was shown at all :s
This is resize function code at the moment which does scaling:
void GLRenderer::resize() {
RECT rect;
int width, height;
GLfloat aspect;
GetClientRect(hWnd, &rect);
width = rect.right;
height = rect.bottom;
if (height == 0) {
height = 1;
}
aspect = (GLfloat) width / height;
glViewport(0, 0, width, height);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluPerspective(45.0, aspect, 0.1, 100.0);
glMatrixMode(GL_MODELVIEW);
}
And my function to render a simple triangle:
void GLRenderer::render() {
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glLoadIdentity();
glTranslated(0, 0, -20);
glBegin(GL_TRIANGLES);
glColor3d(1, 0, 0);
glVertex3d(0, 1, 0);
glVertex3d(1, -1, 0);
glVertex3d(-1, -1, 0);
glEnd();
SwapBuffers(hDC);
}
You can change the zoom in y (height) with the "field of view" parameter to gluPerspective. The one that is 45 degrees in your code. As it is currently always 45 degrees, you will always get the same view angle (in y). How to change this value as a function of the height of the window is not obvious. A linear relation would fail for big values (180 degrees and up). I would try to use arctan(height/k), where 'k' is something like 500.
Notice also that when you extend the window in x, you will already get what you want (the way your source code currently is). That is, you get a wider field of view. That is because you change the aspect (second argument) to a value depending on the ratio between x and y.
Height and Width is measured in pixels, so a value of 1 is not good.
Notice that you are using deprecated legacy OpenGL. See Legacy OpenGL for more information.
How to move a 2D object in the direction of a point (not a GL_POINTS, but coordinates) using OpenGL?
For a better understanding of my code:
I've splited most of my code into different source codes, but this is the one that is actually creating the shapes and setting the scene:
void setupScene(int clearColor[]) {
glClearColor(clearColor[0], clearColor[1], clearColor[2], clearColor[3]);
//glClearColor(250, 250, 250, 1.0); // Set the cleared screen colour to black.
glViewport(0, 0, WINDOW_WIDTH, WINDOW_HEIGHT); // This sets up the viewport so that the coordinates (0, 0) are at the top left of the window.
// Set up the orthographic projection so that coordinates (0, 0) are in the top left.
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glOrtho(0, WINDOW_WIDTH, WINDOW_HEIGHT, 0, -10, 10);
// Back to the modelview so we can draw stuff.
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); // Clear the screen and depth buffer.
}
void drawScene() {
setupScene((int[]){250, 250, 250, 1});
triangle(210, WINDOW_WIDTH, WINDOW_HEIGHT);
glBegin(GL_QUADS);
glColor3f(RGB(80), RGB(80), RGB(80));
glPushMatrix();
glTranslatef(400, 400, 0);
glVertex2d(200, 100);
glVertex2d(100, 100);
glVertex2d(100, 200);
glVertex2d(200, 200);
glPopMatrix();
glEnd();
glutSwapBuffers(); // Send the scene to the screen.
}
void update(int value) {
glutPostRedisplay(); // Tell GLUT that the display has changed.
glutTimerFunc(25, update, 0); // Tell GLUT to call update again in 25 milliseconds.
}
You need to translate the modelview matrix. Assuming you're in modelview mode already:
glPushMatrix();
glTranslatef(x, y, z);
// Draw your shape
glPopMatrix();
[Edit]
#paddy: Something like this? I tried this but the square isn't moving.
pastebin.com/2PCsy5kC
Try explicitly selecting the modelview matrix. Your example does not tell us which mode it's currently in:
glSetMatrixMode(GL_MODELVIEW);
glPushMatrix();
glTranslatef(x, y, z);
// Draw your shape
glPopMatrix();
Normally at the beginning of your render you reset everything... So you enter the GL_PROJECTION mode, call glLoadIdentity() to reset it and set up your camera, then do this for the GL_MODELVIEW matrix as well.
Answer on the behalf of the OP:
Thanks #paddy, I was trying to understand the use of glTranslatef and came with the solution. Here is the working code, it will create a square at 100x100 and will move it until 400x200:
void setupScene(int clearColor[]) {
glClearColor(clearColor[0], clearColor[1], clearColor[2], clearColor[3]);
//glClearColor(250, 250, 250, 1.0); // Set the cleared screen colour to black.
glViewport(0, 0, WINDOW_WIDTH, WINDOW_HEIGHT); // This sets up the viewport so that the coordinates (0, 0) are at the top left of the window.
// Set up the orthographic projection so that coordinates (0, 0) are in the top left.
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glOrtho(0, WINDOW_WIDTH, WINDOW_HEIGHT, 0, -10, 10);
// Back to the modelview so we can draw stuff.
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); // Clear the screen and depth buffer.
}
int a = 100;
int b = 200;
int x = 100;
int y = 100;
void drawScene() {
setupScene((int[]){250, 250, 250, 1});
triangle(210, WINDOW_WIDTH, WINDOW_HEIGHT);
glPushMatrix();
glTranslatef(x, y, 0);
glBegin(GL_QUADS);
glColor3f(RGB(80), RGB(80), RGB(80));
glVertex2d(b, a);
glVertex2d(a, a);
glVertex2d(a, b);
glVertex2d(b, b);
glEnd();
glPopMatrix();
glutSwapBuffers(); // Send the scene to the screen.
}
void update(int value) {
if (x != 400 && y != 200) {
x += 4;
y += 2;
}
glutPostRedisplay(); // Tell GLUT that the display has changed.
glutTimerFunc(25, update, 0); // Tell GLUT to call update again in 25 milliseconds.
}
I am trying to set up a Picture in picture style "map" display for a graphics program that displays a car. (Just shows the view from top again in a smaller view port.) However, the second viewport seems to flicker. I thought I was doing this correctly, but I may be not conceptualizing this correctly.
void display(void) {
glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT|GL_STENCIL_BUFFER_BIT);
// Set Perspective
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluPerspective(fov, aspect, near, far);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
glViewport(0, 0, 500, 500);
// Lighting follows Camera if inserted here.
//Set Camera
calculateCamera();
gluLookAt(eyeX + carPosX, eyeY + carPosY, eyeZ + carPosZ, cX + carPosX,
cY + carPosY, cZ + carPosZ, 0, 1, 0);
displayEnvironment();
glClear(GL_DEPTH_BUFFER_BIT);
// Set Perspective
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluPerspective(fov, aspect, near, far);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
glViewport(0,0,150,150);
gluLookAt(0, 140, 0,0, 0, 0, 1, 0, 0);
displayEnvironment();
}
Where/when are you swapping buffers? Maybe you're not waiting for the render to finish?