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Shader Problems in C

Started by AndyEsser Jan 16, 2008 at 8:30 AM 4 replies 3.9k views

Original Post

Jan 16, 2008 at 8:30 AM

I'm trying to get shaders working in my C OpenGL program. Below is all the code pertaining to the shaders for my program.

[source lang=c]
// Header File For Loading and Executing GLSL Shader Files
#define __ARB_ENABLE true
// #define EXT_INFO
#define MAX_EXTENSION_SPACE 10240
#define MAX_EXTENSION_LENGTH 256
bool multitextureSupported=false;
bool useMultitexture=true;
GLint maxTexelUnits=1;

PFNGLCREATEPROGRAMPROC glCreateProgram = NULL;
PFNGLATTACHSHADERPROC glAttachShader = NULL;
PFNGLLINKPROGRAMPROC glLinkProgram = NULL;
PFNGLUSEPROGRAMPROC glUseProgram = NULL;
PFNGLCREATESHADERPROC glCreateShader = NULL;
PFNGLSHADERSOURCEPROC glShaderSource = NULL;
PFNGLCOMPILESHADERPROC glCompileShader = NULL;

void loadExtensions()
{
	glCreateProgram = (PFNGLCREATEPROGRAMPROC) wglGetProcAddress("glCreateProgram");
	glAttachShader  = (PFNGLATTACHSHADERPROC)  wglGetProcAddress("glAttachShader");
	glLinkProgram   = (PFNGLLINKPROGRAMPROC)   wglGetProcAddress("glLinkProgram");
	glUseProgram    = (PFNGLUSEPROGRAMPROC)    wglGetProcAddress("glUseProgram");
	glCreateShader	= (PFNGLCREATESHADERPROC)  wglGetProcAddress("glCreateShader");
	glShaderSource  = (PFNGLSHADERSOURCEPROC)  wglGetProcAddress("glShaderSource");
	glCompileShader = (PFNGLCOMPILESHADERPROC) wglGetProcAddress("glCompileShader");

	GLuint v = glCreateShader(GL_VERTEX_SHADER);
	GLuint f = glCreateShader(GL_FRAGMENT_SHADER);
	GLuint p = glCreateProgram();
	char buffer[50];
	sprintf(buffer,"Creating Shader Program(ID:%i)",p);
	writeLog(buffer,"",TRUE);

	FILE *file;
	FILE *debug;
	sprintf(buffer,"Creating Vertex Shader(ID:%i)",v);
	if((file=fopen("Data\\Shaders\\vertex.shader","r"))==NULL)
	{
		writeLog(buffer,"",FALSE);
	} else {
		char vShaderSource[500];
		fscanf(file,vShaderSource);
		fclose(file);
		const GLchar * vs = vShaderSource;
		debug=fopen("shaderLog.txt","w");
		fputs(vs,debug);
		fclose(debug);
		glShaderSource(v,1,&vs,NULL);
		writeLog(buffer,"",TRUE);		
	}
	
	sprintf(buffer,"Creating Fragment Shader(ID:%i)",f);
	if((file=fopen("Data\\Shaders\\fragment.shader","r"))==NULL)
	{
		writeLog(buffer,"",FALSE);
	} else {
		char fShaderSource[500];
		fscanf(file,fShaderSource);
		fclose(file);

		const GLchar * fs = fShaderSource;
		glShaderSource(f,1,&fs,NULL);
		writeLog(buffer,"",TRUE);
	}

	glAttachShader(p,v);
	glAttachShader(p,f);

	glLinkProgram(p);

	glUseProgram(p);
}

On my computer the program still runs, but I know it's not using the shaders, because if I introduce an easily visible error, nothing changes. On some computers it just crashes out. Any suggestions? Cheers

V-man

Jan 16, 2008 at 8:53 AM

It's better to have some package get the function pointers for you.
http://www.opengl.org/wiki/index.php/Getting_started

"OpenGL 2.0 and extensions" section explains what to do.

Quote:
On my computer the program still runs, but I know it's not using the shaders, because if I introduce an easily visible error, nothing changes. On some computers it just crashes out.

Put safety in your code. Don't let it crash.
Check to see that at least GL 2.0 is supported.

smitty1276

Jan 16, 2008 at 9:21 AM

You can also use functions like glInfoLogARB (I think it is called) to get error messages from the GLSL compiler/linker, etc.

KumGame07

Jan 16, 2008 at 10:21 PM

As V-man suggested you need to put safety codes. I think your shaders are not compiling fine. There are chances that the shader source that you are providing to GL is NULL as your 'fscanf' looks pretty strange to me.

AndyEsser

Jan 17, 2008 at 3:43 AM

Any chance of a hint as to the correct code to load the text from the file?

KumGame07

Jan 17, 2008 at 10:09 PM

Google it. You get plenty of resources for file reading in C.
Anyways let me tell you what I do for reading shaders

if (fileName){		FILE *filePtr = fopen(fileName, "r");		fseek(filePtr, 0, SEEK_END);		fileSize = ftell(filePtr);		// Reset the file pointer to the beginning		fseek(filePtr, 0, SEEK_SET);				// Allocate memory		source = (char *)malloc(sizeof(char) * fileSize + 1);		// Read at once		fread(source, sizeof(char), fileSize, filePtr);		source[fileSize] = '\0';		// have a null terminated string}

EDIT : modified the code

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