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A Few Questions Regarding OpenGL


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#1 Toothpix   Crossbones+   -  Reputation: 810

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Posted 10 February 2013 - 04:09 PM

I recently started creating my first shader-based OpenGL program in a limited subset of 3.2, but can you have more than one program object? I created a program object for both the vertex and fragment shaders, and attached their respective shaders to them and linked them. I started the entire program (after windowing and contexts) with the createShader function, then I compiled and attached to program, then the same for the fragment shader. Am I starting correctly?
 
Also, is OpenGL 3.2 easily portable to ES 2 if I use no geometry shaders? What if I do?
 P.S: Here is my rendering source code thus far:
 
#include <windows.h>
#include <GL/glew.h>
#include <GL/glext.h>
#include <GL/gl.h>
#include "renderMain.h"
#include "fileAccess.h"

#define ULONG unsigned long

renderMain()
{
    /* Creating and Compiling the Primary Vertex Shader */
    GLuint vertShader = 0;
    vertShader = glCreateShader(VERTEX_SHADER);
    glShaderSource(vertShader, /*insert parameter*/ , /*insert parameter*/);
    glCompileShader(vertShader);

    /* Creating and Compiling the Primary Fragment Shader */
    GLuint fragShader = 0;
    fragShader = glCreateShader(FRAGMENT_SHADER);
    glShaderSource(fragShader, /*insert parameter*/ , /*insert parameter*/);
    glCompileShader(fragShader);

    /* Creating Vertex Program */
    GLuint progObjVert = 0;
    progObjVert = glCreateProgram();
    glAttachShader(progObjVert, vertShader);

    /* Creating Fragment Program */
    GLuint progObjFrag = 0;
    progObjFrag = glCreateProgram();
    glAttachShader(progObjVert, fragShader);
}

 

 

Where I put the "insert parameter" comments is where I will use pointers from the fileAccess source file to get shaders from a file. Also, this is called from main() which is in main.c, which is where all of the windowing and context handling is. But is this the proper way to start out? I can add main.c if that is important.


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#2 TheChubu   Crossbones+   -  Reputation: 3600

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Posted 10 February 2013 - 04:32 PM

You should attach to a program all you want to use for your draw call.

 

The fragments are created out of the projection of the geometry in the vertex shader. How your program that has the fragment shader will access the data that your first program with the vertex shader processed? 

 

In a single program you attach all you need (vertex, fragment, etc). And then you can make your draw call that will use the shaders that you linked to your program.

 

Now, you can use several programs because not all things are drawn the same, ie, not everything uses the same shader.


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