Thanks to stack overflow I am very close to figuring out lots of problems I've been having. I got one more for this weekend.
I have an object called GameObject2D that is basically a square with some textures. Everything works when projecting this object in 3D. I use a method called prepare3Ddrawing to do this. I then want to do 2D drawing so I have a I am using a method to prep the projection matrix for 2d drawing. I've tried two different versions of the prepare2Ddrawing and can't seam to get it to work. First here is my 3d prep...
private void prepare3Ddrawing(GL10 gl)
{
gl.glLoadIdentity();
gl.glViewport(0, 0, getWidth(), getHeight());
gl.glDisable(GL10.GL_DITHER);
gl.glEnable(GL10.GL_DEPTH_TEST);
gl.glMatrixMode(GL10.GL_PROJECTION);
gl.glLoadIdentity();
GLU.gluPerspective(gl, 45.0f, (float)getWidth()/(float)getHeight(),0.1f,100.0f);
}
And here is the version of my 2D that puts the origin at the bottom left instead of the top left...
private void prepare2Ddrawing(GL10 gl)
{
gl.glDisable(GL10.GL_DEPTH_TEST);
gl.glLoadIdentity();
gl.glMatrixMode(GL10.GL_PROJECTION);
gl.glLoadIdentity();
GLU.gluOrtho2D(gl,0,getWidth(), 0, getHeight());
gl.glMatrixMode(GL10.GL_MODELVIEW);
gl.glLoadIdentity();
}
I believe I need the right combination of GLU.gluOrtho2D(gl...) to get the right result. Any ideas? Thanks!
GLU.gluOrtho2D(gl,0,getWidth(), 0, getHeight()) has parameters left, right, bottom, top. If you want "screen-like" coordinates you need to set top to "0.0" and bottom to "getHeight()". This method is basically used to setup your coordinate system. For instance, if you need to draw some graph you would want the (0,0) in center, left if (-1,0) and top is (0,1) so the parameters would be (-1, 1,-1, 1) but if you want to have something like most common screen coordinate system you will want to have (0,0) in top left corner and (width, height) in bottom right corner (0, width, height, 0). Or for the sake of simplicity: Just insert the coordinates you want at top-left and bottom-right points of your view.
Related
I am new to OpenGL, and have recently successfully drawn my first shapes with the guide on the Android Developers website. Right now I am trying to only focus on the upper half of the graph on my OpenGL 2D rendering. So as you guys know, right smack in the middle of the screen is (0,0). However now I want the origin to be at the middle of the bottom of the screen, while maintaining the y axis 0.5f value to be at the middle of the screen and 1f at the top of the screen. In essence, the negative y axis portion is not in view.
These are the coordinates of my square:
float squareCoords[] = {
// x , y , z
-0.5f, 0.5f , 0.0f //top left
-0.5f, 0f , 0.0f //bottom left
0.5f, 0f , 0.0f //bottom right
0.5f, 0.5f , 0.0f //top right
};
This is how I want the square to look on the screen
Ive tried using the camera to focus view but it makes the view bigger(the max y-value and x-value increases, and the object becomes smaller) in the renderer class:
Matrix.setLookAtM(viewMatrix,0,0,0.5f,3,0f,0.5f,0f,0f,1.0f,0.0f)
Does it have something to with GLES20.glViewport? The best I can come up with from online research is a function ortho2d() but it seems like Android Studio does not support it. Any help appreciated.Thanks!
You can use Matrix.orthoM
Matrix.orthoM(
projectionMatrix, 0,
left, right,
bottom, top,
near, far
);
And multiply it with viewMatrix set with Matrix.setLookAtM to obtain View-Projection matrix:
Matrix.multiplyMM(
vpMatrix, 0,
projectionMatrix, 0, viewMatrix, 0
);
Then use vpMatrix in your shader
void main() {
gl_Position = u_VpMatrix * a_Position;
}
...
int uVpMatrix = glGetUniformLocation(program, "u_VpMatrix");
...
glUniformMatrix4fv(uVpMatrix, 1, false, vpMatrix, 0);
Found the soln after further trial and error
In the renderer class at onSurfaceChanged(GL10 unused, int width ,int height){
//edit the Matrix.frustumM method, value for parameter bottom should be set to 0
Matrix.frustumM(projectionMatrix,0,left,right,bottom,top,near,far)
}
Should help with people who want to change the position of their origins to any other location as well, simply change the left,right,top,bottom values.
or refer to this stackoverflow: Set origin to top-left corner of screen in OpenGL ES 2
for other possible solutions.
I am drawing an image based texture using opengl in android and trying to rotate it about its center.
But the result is not as expected and it appears skewed.
First screen grab is the texture drawn without rotation and the second one is the one drawn with 10 degree rotation.
Code snippet is as below:
mViewWidth = viewWidth;//View port width
mViewHeight = viewHeight;//View port height
float ratio = (float) viewWidth / viewHeight;
Matrix.frustumM(mProjectionMatrix, 0, -ratio, ratio, -1, 1, 3, 7);
.....
Matrix.setLookAtM(mViewMatrix, 0, 0, 0, 5, 0f, 0f, 0f, 0.0f, 1.0f, 0.0f);
Matrix.setRotateM(mRotationMatrix, 0, 10, 0, 0, 1.0f);
Matrix.multiplyMM(temp, 0, mProjectionMatrix, 0, mViewMatrix, 0);
Matrix.multiplyMM(mMVPMatrix, 0, temp, 0, mRotationMatrix, 0);
GLES20.glUniformMatrix4fv(mRotationMatrixHandle , 1, false, mRotationMatrix, 0);
And in shader:
....
" gl_Position = uMVPMatrix*a_position;\n"
....
The black area in the first screen grab is the area of GLSurfaceView and the grey area is the area where I am trying to draw the image.
The image is already at origin and I think there is no need to translate before rotating it.
The basic problem is that you're scaling your geometry to adjust for the screen aspect ratio before you apply the rotation.
It might not be obvious that you're actually scaling the geometry. But by calculating the coordinates you use for drawing to adjust for the aspect ratio, you are effectively applying a non-uniform scaling transformation to the geometry. And if you then rotate the result, it will get distorted.
What you need to do is apply the rotation before you scale. This will require some reorganization of your current code. Since you apply the scaling before you pass the coordinates to OpenGL, and then do the rotation in the shader, you can't easily change the order. You either have to:
Apply both transformations, in the proper order, to the input coordinates before you pass them to OpenGL, and remove the rotation from the shader code.
Apply both transformations, in the proper order, in the shader code. To do this, you would not modify the input coordinates to adjust to the aspect ratio, and pass a scaling factor into the shader instead.
For the first option, applying a 2D rotation in your own code is easy enough, and it looks like you only have 4 vertices, so there is no efficiency concern. Still the second options is certainly more elegant. So instead of scaling the coordinates in your client code, pass a scaling factor as a uniform into the shader. Then, in the GLSL code, apply the rotation first, and scale the resulting coordinates.
Another option is that you build the complete transformation matrix (again based on applying the individual transformations in the correct order), and pass that matrix into the shader.
I'm trying to make 2D graphics for my Android app that consists of six thin rectangles that each take up about 1/6th of the screen in width and equal the screen's height. I'm not sure the right way to determine the bounds of the x and y OpenGL coordinate plane on screen. Eventually I will need to write logic that tests which of the 6 rectangles a touch event occurs in, so I have been trying to solve this problem by remapping OpenGL's coordinate plane into the device's screen coordinate plane (where the origin (0,0) is at the top left of the screen instead of the middle.
I declare one of my six rectangles like so:
private float vertices1[] = {
2.0f, 10.0f, 0.0f, // 0, Top Left
2.0f, -1.0f, 0.0f, // 1, Bottom Left
4.0f, -1.0f, 0.0f, // 2, Bottom Right
4.0f, 10.0f, 0.0f, // 3, Top Right
};
but since i'm not sure what the visible limits are on the x and y planes (in the OpenGL coordinate system) I have no concrete way of knowing what vertices my rectangle needs to be instantiated with to occupy 1/6th of the display. Whats the ideal way to do this?
I've tried approaches such as using glOrthoof() to remap OpenGL's coordinates into easy to work with device screen coordinates:
gl.glViewport(0, 0, width, height);
// Select the projection matrix
gl.glMatrixMode(GL10.GL_PROJECTION);
// Reset the projection matrix
gl.glLoadIdentity();
// Calculate the aspect ratio of the window
GLU.gluPerspective(gl, 45.0f,(float) width / (float) height,0.1f, 100.0f);
gl.glOrthof(0.0f,width,height, 0.0f, -1.0f, 5.0f);
// Select the modelview matrix
gl.glMatrixMode(GL10.GL_MODELVIEW);
// Reset the modelview matrix
gl.glLoadIdentity();
but when I do my rectangle dissapears completely.
You certainly don't want to use a perspective projection for 2D graphics. That just doesn't make much sense. A perspective projection is for... well, creating a perspective projection, which is only useful if your objects are actually placed in 3D space.
Even worse, you have two calls to set up a perspective matrix:
GLU.gluPerspective(gl, 45.0f,(float) width / (float) height,0.1f, 100.0f);
gl.glOrthof(0.0f,width,height, 0.0f, -1.0f, 5.0f);
While that's legal, it rarely makes sense. What essentially happens if you do this is that both projections are applied in succession. So the first thing to do is get rid of the gluPerspective() call.
To place your 6 rectangles, you have a few options. Almost the easiest one is to not apply any transformations at all. This means that you will specify your input coordinates in normalized device coordinates (aka NDC), which is a range of [-1.0, 1.0] in both the x- and y-direction. So for 6 rectangles rendered side by side, you would use a y-range of [-1.0, 1.0] for all the rectangles, and an x-range of [-1.0, -2.0/3.0] for the first, [-2.0/3.0, -1.0/3.0] for the second, etc.
Another option is that you use an orthographic projection that makes specifying the rectangles even more convenient. For example, a range of [0.0, 6.0] for x and [0.0, 1.0] for y would make it particularly easy:
gl.glOrthof(0.0f, 6.0f, 0.0f, 1.0f, -1.0f, 1.0f);
Then all rectangles have a y-range of [0.0, 1.0], the first rectangle has a x-range of [0.0, 1.0], the second rectangle [1.0, 2.0], etc.
BTW, if you're just starting with OpenGL, I would pass on ES 1.x, and directly learn ES 2.0. ES 1.x is a legacy API at this point, and I wouldn't use it for any new development.
how can I make it so I can plug in pixel coordinates into gl.glTranslatef() ?
Currently, I do this to get the texture appear at the bottom of the screen:
gl.glPushMatrix();
gl.glTranslatef(1.45f, -2.76f, 0);
gl.glScalef(1 / scaleX, 1 / scaleY, 0);
Square sq = getTexture(resourceId);
sq.draw(gl);
gl.glPopMatrix();
Without having to plug in the "1.45f, -2.76f, 0" values, the texture appears at the centre of the screen. How can I position my textures using pixel coordinates? Most of my texture's dimensions are 32x32, and a few 16x16.
Before I have used ((GL11Ext) gl).glDrawTexfOES() to render my textures, however I was unable to perform any transformations to the textures, for example I couldn't rotate them, etc.
I don't know how you set up your projection, but what you should be doing is use glOrtho and glViewport to set up your scene. given a window of size (width, height):
// init opengl at some previous point
gl.glViewport(0, 0, width, height);
// choose bottom-left corner, e.g. (0,0)
// use your own values for near and far planes
float left = 0, bottom = 0, near = 0.1f, far = 1000.0f;
gl.glMatrixMode(GL_PROJECTION);
gl.glOrtho(left, left + width, bottom, bottom + height, near, far);
gl.glMatrixMode(GL_MODELVIEW);
gl.glLoadIdentity();
and you will get pixel-coords (bottom-left at (left,bottom)) for your application
I am trying to understand the basic concepts around the co-ordinates system in OpenGL so I have been making a test application from guides online.
Presently I have drawn a simple Square to the screen, using simple Co-ordinates of:
-1.0f, 1.0f, 0.0f, // 0, Top Left
-1.0f, -1.0f, 0.0f, // 1, Bottom Left
1.0f, -1.0f, 0.0f, // 2, Bottom Right
1.0f, 1.0f, 0.0f, // 3, Top Right
In my application I run the following code:
GLU.gluPerspective(gl, 45.0f, (float) width / (float) height, 0.1f, 100.0f);
My basic understanding here is that the code is setting the viewing port angle to 45 degrees and the width to height ratio of the window size.
Another thing I am doing is setting the viewing position as -4 units on the Z axis:gl.glTranslatef(0, 0, -4);
This is what the result looks like in Landscape...
And in Portrait...
My questions are:
How does the co-ordinate system work, how many Pixels does one unit represent? How does changing the orientation and width to height ratio effect the equation?
If I wanted to draw a square the size of the screen, with a View Port of 45 degrees and a Viewing position of z-4... how does one figure out the required width and height in units?
I'll try to answer the best I can.
There wouldn't be any reason to change the width to height ratio or 45 degree angle. Doing it the way you have it keeps the things from being stretched horizontally or vertically in an unusual way. Because you are using a perspective view, you have 3D space with depth as apposed to an Orthographic view where there is no depth. In doing glTranslatef(0,0,-4) what you've actually done is changed the MODELVIEW Matix, moving it 4 in the negative z direction, presumably before actually drawing the square. By default, the "camera" is sitting at 0,0,0 with Y (up) as the upward direction.
You may be able to translate 3D space to pixels, but with a Perspective view type, I'm not at all sure you'd really want or need to. A 2D Orthographic view would be a different story, though, as many people use OpenGL for 2D games as well. Wanting a square exactly the size of the screen, Orthographic is probably the way to go, and you should be able to with a few Google searches be able to figure out your pixel density to 2d space comparison.