# OpenGL New to OpenGL, some issues

## Recommended Posts

I am new to OpenGL (and graphics programming in general).

I am working through Daniel Schuller's 'C# Game Programming for Serious Game Creation'.

Some of the examples in the book are not behaving the way the book indicates.  I want to figure out if I am doing something wrong or the book is.

I have a simple rotating triangle method:

float width=0.5;

Gl.glClearColor(0.0f, 0.0f, 0.0f, 1.0f);
Gl.glClear(Gl.GL_COLOR_BUFFER_BIT);
Gl.glPointSize(5.0f);

Gl.glRotated(_currentRotation, 0, 1, 0);
Gl.glBegin(Gl.GL_TRIANGLE_STRIP);
{
Gl.glColor4d(1.0, 0.0, 0.0, 0.5);
Gl.glVertex3d(-width, 0, 0);
Gl.glColor3d(0.0, 1.0, 0.0);
Gl.glVertex3d(width, 0, 0);
Gl.glColor3d(0.0, 0.0, 1.0);
Gl.glVertex3d(0, width, 0);
}
Gl.glEnd();
Gl.glFinish();

I also have a Setup2DGraphics function that gets called on startup and everytime the host form changes size:

private void Setup2DGraphics(double width, double height)
{
Gl.glViewport(0, 0, (int)width, (int)height);
double halfWidth = width / 2;
double halfHeight = height / 2;
Gl.glMatrixMode(Gl.GL_PROJECTION);
Gl.glOrtho(-halfWidth, halfWidth, -halfHeight, halfHeight, -100, 100);
Gl.glMatrixMode(Gl.GL_MODELVIEW);

}

The problem I am having is that no matter what size I change the form to, it seems like the Triangle is being drawn to an openGL space that is -1,1,-1,1.

That is, if I set width on the triangle to 0.5, then I get a triangle that stretches up, left and right half the viewport size.

My understanding (and the way the book presents it) is that if I'm passing in the height and width of the form to Setup2DGraphics function, (using ClientSize.Height and ClientSize.Width properties), that glOrtho will essentially make a 1:1 mapping between the viewport and my form.  But that is not happening.  No matter the size of the form, the triangle scales to the window size even as the width stays constant at 0.5.  If I make width, say, 50, then it stretches vastly off the viewport.

So what am I missing/doing wrong here?

##### Share on other sites

The obvious cause of the described effect is that the projection matrix isn't set. Common reasons are because the setup function isn't called, it is called before the window and the rendering context is created, or because the projection matrix is reset at some later point.

Edited by Brother Bob

##### Share on other sites

The obvious cause of the described effect is that the projection matrix isn't set. Common reasons are because the setup function isn't called, it is called before the window and the rendering context is created, or because the projection matrix is reset at some later point.

I think you are right.  I've done some experimenting and it seems that is what is happening.  I'll figure out why.

Thanks!

## Create an account

Register a new account

• ### Forum Statistics

• Total Topics
627763
• Total Posts
2978974
• ### Similar Content

• Hello! As an exercise for delving into modern OpenGL, I'm creating a simple .obj renderer. I want to support things like varying degrees of specularity, geometry opacity, things like that, on a per-material basis. Different materials can also have different textures. Basic .obj necessities. I've done this in old school OpenGL, but modern OpenGL has its own thing going on, and I'd like to conform as closely to the standards as possible so as to keep the program running correctly, and I'm hoping to avoid picking up bad habits this early on.
Reading around on the OpenGL Wiki, one tip in particular really stands out to me on this page:
For something like a renderer for .obj files, this sort of thing seems almost ideal, but according to the wiki, it's a bad idea. Interesting to note!
So, here's what the plan is so far as far as loading goes:
Set up a type for materials so that materials can be created and destroyed. They will contain things like diffuse color, diffuse texture, geometry opacity, and so on, for each material in the .mtl file. Since .obj files are conveniently split up by material, I can load different groups of vertices/normals/UVs and triangles into different blocks of data for different models. When it comes to the rendering, I get a bit lost. I can either:
Between drawing triangle groups, call glUseProgram to use a different shader for that particular geometry (so a unique shader just for the material that is shared by this triangle group). or
Between drawing triangle groups, call glUniform a few times to adjust different parameters within the "master shader", such as specularity, diffuse color, and geometry opacity. In both cases, I still have to call glBindTexture between drawing triangle groups in order to bind the diffuse texture used by the material, so there doesn't seem to be a way around having the CPU do *something* during the rendering process instead of letting the GPU do everything all at once.
The second option here seems less cluttered, however. There are less shaders to keep up with while one "master shader" handles it all. I don't have to duplicate any code or compile multiple shaders. Arguably, I could always have the shader program for each material be embedded in the material itself, and be auto-generated upon loading the material from the .mtl file. But this still leads to constantly calling glUseProgram, much more than is probably necessary in order to properly render the .obj. There seem to be a number of differing opinions on if it's okay to use hundreds of shaders or if it's best to just use tens of shaders.
So, ultimately, what is the "right" way to do this? Does using a "master shader" (or a few variants of one) bog down the system compared to using hundreds of shader programs each dedicated to their own corresponding materials? Keeping in mind that the "master shaders" would have to track these additional uniforms and potentially have numerous branches of ifs, it may be possible that the ifs will lead to additional and unnecessary processing. But would that more expensive than constantly calling glUseProgram to switch shaders, or storing the shaders to begin with?
With all these angles to consider, it's difficult to come to a conclusion. Both possible methods work, and both seem rather convenient for their own reasons, but which is the most performant? Please help this beginner/dummy understand. Thank you!

• I want to make professional java 3d game with server program and database,packet handling for multiplayer and client-server communicating,maps rendering,models,and stuffs Which aspect of java can I learn and where can I learn java Lwjgl OpenGL rendering Like minecraft and world of tanks

• A friend of mine and I are making a 2D game engine as a learning experience and to hopefully build upon the experience in the long run.

-What I'm using:
C++;. Since im learning this language while in college and its one of the popular language to make games with why not.     Visual Studios; Im using a windows so yea.     SDL or GLFW; was thinking about SDL since i do some research on it where it is catching my interest but i hear SDL is a huge package compared to GLFW, so i may do GLFW to start with as learning since i may get overwhelmed with SDL.
-Questions
Knowing what we want in the engine what should our main focus be in terms of learning. File managements, with headers, functions ect. How can i properly manage files with out confusing myself and my friend when sharing code. Alternative to Visual studios: My friend has a mac and cant properly use Vis studios, is there another alternative to it?

• 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.

• 11
• 10
• 10
• 23
• 14