OpenGL Orthogonal matrix issue

Recommended Posts

Hello everyone.

I've ran into a strange issue in my engine. With openGL ES 2.0, when I render my scene with a projection matrix, my scene renders correctly. With a orthogonal matrix, nothing renders at all. I'm using my own projection matrix functions to generate the matrices, so naturally, my first suspicion would be that my orthogonal matrix is being constructed erroneously but even openGL's orthoM() function bears the same problem.

Here is my GLSL vertex shader.

[code]
uniform mat4 u_projection_matrix;
uniform mat4 u_view_matrix;
uniform mat4 u_model_matrix;
attribute vec3 a_position;
attribute vec3 a_normal;
attribute vec2 a_texCoord0;
varying vec2 v_texCoord0;

void main()
{
v_texCoord0 = a_texCoord0;
gl_Position = ((u_projection_matrix * u_view_matrix * u_model_matrix) * vec4(a_position.xyz, 1.0));
}
[/code]

Here is my orthogonal projection matrix generation function just in case..

[code]
public void CreateOrthoMatrix(float left, float right, float bottom, float top, float near, float far)
{
// These paramaters are lens properties.
// The "near" and "far" create the Depth of Field.
// The "left", "right", "bottom" and "top" represent the rectangle formed
// by the near area, this rectangle will also be the size of the visible area.

Matrix.setIdentityM(projectionMatrix, 0);

// First Column
projectionMatrix[0] = 2.0f / (right - left);
projectionMatrix[1] = 0.0f;
projectionMatrix[2] = 0.0f;
projectionMatrix[3] = 0.0f;

// Second Column
projectionMatrix[4] = 0.0f;
projectionMatrix[5] = 2.0f / (top - bottom);
projectionMatrix[6] = 0.0f;
projectionMatrix[7] = 0.0f;

// Third Column
projectionMatrix[8] = 0.0f;
projectionMatrix[9] = 0.0f;
projectionMatrix[10] = -2.0f / (far - near);
projectionMatrix[11] = 0.0f;

// Fourth Column
projectionMatrix[12] = (right + left) / (right - left);
projectionMatrix[13] = (top + bottom) / (top - bottom);
projectionMatrix[14] = (far + near) / (far - near);
projectionMatrix[15] = 1;
}
[/code]

Anyone have any ideas whats going on?

My appreciations.

Share on other sites
Try

[code] // Fourth Column
projectionMatrix[12] = -(right + left) / (right - left);
projectionMatrix[13] = -(top + bottom) / (top - bottom);
projectionMatrix[14] = -(far + near) / (far - near);
projectionMatrix[15] = 1; [/code]

Share on other sites
[quote name='NumberXaero' timestamp='1312667268' post='4845560']
Try

[code] // Fourth Column
projectionMatrix[12] = -(right + left) / (right - left);
projectionMatrix[13] = -(top + bottom) / (top - bottom);
projectionMatrix[14] = -(far + near) / (far - near);
projectionMatrix[15] = 1; [/code]
[/quote]

Thank you, but still no go after replacing my fourth column code the code you posted . If it helps this is how I call the method.

[code]
CreateOrthoMatrix(0.0f, width, 0.0f, height, 0.1f, 100f);
[/code]

Where the width and height is the width and height of my viewport. Which are matched to the pixel width and height of my device's screen.

Share on other sites
Switching from a perspective to orthogonal matrix sometimes isn't simply as easy as changing the matrix. You also have to look at the scale of things that were being drawn before, and how they are being drawn now. Some objects might be too large, some might be too small, etc... For instance, a very small object (say, less than 1 unit in length/width/height) would occupy a large portion of the screen if viewed through a projection matrix, if it were close enough to the camera. However, with an orthogonal matrix, regardless of how near the camera it is, that object would always be drawn as less than one pixel in size (given a 1:1 mapping of projection space to screen space) since it's real size is less than one.

I'd say, test out your projection code with a controllable test case first, before you switch your in-project matrix, then when you are assured the matrix code is working correctly, begin the process of switching your game over.

Share on other sites
[quote name='JTippetts' timestamp='1312673160' post='4845601']
Switching from a perspective to orthogonal matrix sometimes isn't simply as easy as changing the matrix. You also have to look at the scale of things that were being drawn before, and how they are being drawn now. Some objects might be too large, some might be too small, etc... For instance, a very small object (say, less than 1 unit in length/width/height) would occupy a large portion of the screen if viewed through a projection matrix, if it were close enough to the camera. However, with an orthogonal matrix, regardless of how near the camera it is, that object would always be drawn as less than one pixel in size (given a 1:1 mapping of projection space to screen space) since it's real size is less than one.

I'd say, test out your projection code with a controllable test case first, before you switch your in-project matrix, then when you are assured the matrix code is working correctly, begin the process of switching your game over.
[/quote]

jTippetts, Extrodenary Information!! I am making my engine unit relative to the metric meter. Yet I was contructing my orthogonal projection matrix's bounds to be relative to pixils, so everything in the scene was way too small. I am glad to now know that aspect in the nature of working with an othrogonal projection matrix.

NumberXaero, Thank you as well! That fixed up the implementation of my orthogonal projection matrix and now it works!

Thanks guys, you both saved me boat loads of time and made my day!

[b]
[/b]

Share on other sites
You might want to consider using glm.
http://glm.g-truc.net/
It is a really nice math library for Vectors and Matrices especially designed for OpenGL and written against the GLSL ShaderSpec.
It saved [b]me[/b] a lot of time implementing that on my own.

Share on other sites
Hidden
How do I increase your ratings these days? The like button?

[quote name='NicoG' timestamp='1312675908' post='4845611']
You might want to consider using glm.
[url="http://glm.g-truc.net/"]http://glm.g-truc.net/[/url]
It is a really nice math library for Vectors and Matrices especially designed for OpenGL and written against the GLSL ShaderSpec.
It saved [b]me[/b] a lot of time implementing that on my own.
[/quote]

I'll be sure to check it out, thanks!

Create an account

Register a new account

• Partner Spotlight

• Forum Statistics

• Total Topics
627675
• Total Posts
2978572
• 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?

• 11
• 11
• 10
• 12
• 22