# OpenGL Can't understand camera behavior

## Recommended Posts

Hello.

I'm quite new person in OpenGL graphics. Recently I started to learn OpenGL ES 2.0 technology to be able to make some games on my Android devices. I have a few questions to clear some things up for me.

1. Where can I find comprehensive OpenGL ES 2.0 tutorials, or book for making games on Android by means of Java/Android SDK, not C++/NDK? A lot of resources are dedicated to OpenGL ES 1.0 technology, not 2.0 one. In fact it's very hard to find complete tutorials for 2.0 with good non-contradictory code base.

2. Why there are almost no 2.0 tutorials? Is it any popular? Google says that devices starting from Android 2.2 can use this new version, so if no one uses it, why? At the first glance it gives more flexible way of doing things.

3. I'm a bit confused with the way matrix multiplication system works.

Do I have to use:

Matrix.setIdentityM( mModelMatrix, 0 );
Matrix.multiplyMM( mMVPMatrix, 0, mViewMatrix, 0, mModelMatrix, 0 );
Matrix.multiplyMM( mMVPMatrix, 0, mProjectionMatrix, 0, mMVPMatrix, 0 );

To get simple mMVPMatrix = mModelMatrix * mMviewMatrix * mProjectionMatrix equation done? Can I use this result matrix as uniform variable in shader?

4. Is this the right code to rotate my object around Y axis by some angle 'mAngle':

Matrix.setRotateM( mRotationMatrix, 0, mAngle, 0.0f, -1.0f, 0.0f );
Matrix.setIdentityM( mModelMatrix, 0 );
Matrix.multiplyMM( mModelmatrix, 0, mRotationMatrix, 0, mModelMatrix, 0 );
Matrix.multiplyMM( mMVPMatrix, 0, mViewMatrix, 0, mModelMatrix, 0 );
Matrix.multiplyMM( mMVPMatrix, 0, mProjectionMatrix, 0, mMVPMatrix, 0 );

To me it seems legit, but I get really weird results on my phone when I try to render simple textured box. Top, bottom sides of the box rotate around camera, not the opposite way.

This is my renderer and simple textured cube classes:

http://pastebin.com/Phd2ym3Z - renderer

http://pastebin.com/i9rb3r6v - textured cube

Edited by GuardianX

##### Share on other sites

2. It's very popular, because almost all modern games use shaders, and to get shaders with OpenGL ES you must use 2.0 or 3.0 which is not yet widely supported.

3. Yes, you can use the resulting matrix in a shader.

##### Share on other sites

Top, bottom sides of the box rotate around camera, not the opposite way.

You need to translate the box away from the camera before rotating the box. It rotates the box around itself, so if the center of the box is at the camera (like it is without a translation) then it rotates around the camera.

##### Share on other sites

There is not that much gles2.0 spesific in shader or in mobile development in general. Just learn something that you can get to start and then any general shader book will teach you. LibGDX is good start for Java android development and author of that framework is also writed book about Android development http://www.amazon.com/Beginning-Android-Games-Mario-Zechner/dp/1430230428

## Create an account

Register a new account

• ## Partner Spotlight

• ### Forum Statistics

• Total Topics
627661
• Total Posts
2978496
• ### Similar Content

• Both functions are available since 3.0, and I'm currently using glMapBuffer(), which works fine.
But, I was wondering if anyone has experienced advantage in using glMapBufferRange(), which allows to specify the range of the mapped buffer. Could this be only a safety measure or does it improve performance?
Note: I'm not asking about glBufferSubData()/glBufferData. Those two are irrelevant in this case.
• By xhcao
Before using void glBindImageTexture(    GLuint unit, GLuint texture, GLint level, GLboolean layered, GLint layer, GLenum access, GLenum format), does need to make sure that texture is completeness.
• By cebugdev
hi guys,
are there any books, link online or any other resources that discusses on how to build special effects such as magic, lightning, etc. in OpenGL? i mean, yeah most of them are using particles but im looking for resources specifically on how to manipulate the particles to look like an effect that can be use for games,. i did fire particle before, and I want to learn how to do the other 'magic' as well.
Like are there one book or link(cant find in google) that atleast featured how to make different particle effects in OpenGL (or DirectX)? If there is no one stop shop for it, maybe ill just look for some tips on how to make a particle engine that is flexible enough to enable me to design different effects/magic
let me know if you guys have recommendations.
• By dud3
How do we rotate the camera around x axis 360 degrees, without having the strange effect as in my video below?
Mine behaves exactly the same way spherical coordinates would, I'm using euler angles.
Tried googling, but couldn't find a proper answer, guessing I don't know what exactly to google for, googled 'rotate 360 around x axis', got no proper answers.

References:
Code: https://pastebin.com/Hcshj3FQ
The video shows the difference between blender and my rotation:

• By Defend
I've had a Google around for this but haven't yet found some solid advice. There is a lot of "it depends", but I'm not sure on what.
My question is what's a good rule of thumb to follow when it comes to creating/using VBOs & VAOs? As in, when should I use multiple or when should I not? My understanding so far is that if I need a new VBO, then I need a new VAO. So when it comes to rendering multiple objects I can either:
* make lots of VAO/VBO pairs and flip through them to render different objects, or
* make one big VBO and jump around its memory to render different objects.
I also understand that if I need to render objects with different vertex attributes, then a new VAO is necessary in this case.
If that "it depends" really is quite variable, what's best for a beginner with OpenGL, assuming that better approaches can be learnt later with better understanding?

• 10
• 12
• 22
• 13
• 33