hello - Page 807 - Developer IT

Fragment shaders on a texture

- by Snowangelic

Hello stack overflow. I am trying to add some post-processing capabilities to a program. The rendering is done using openGL. I just want to allow the program to load some home made fragment shader and use them on the video stream. I wrote a little piece of shader using "OpenGL Shader Builder" that just turns a texture in grayscale. The shaders works well in the shader builder but I can't make it work in the main program. The screens stays all black. Here is the setup : @implementation PluginGLView - (id) initWithCoder: (NSCoder *) coder { const GLubyte * strExt; if ((self = [super initWithCoder:coder]) == nil) return nil; glLock = [[NSLock alloc] init]; if (nil == glLock) { [self release]; return nil; } // Init pixel format attribs NSOpenGLPixelFormatAttribute attrs[] = { NSOpenGLPFAAccelerated, NSOpenGLPFANoRecovery, NSOpenGLPFADoubleBuffer, 0 }; // Get pixel format from OpenGL NSOpenGLPixelFormat* pixFmt = [[NSOpenGLPixelFormat alloc] initWithAttributes:attrs]; if (!pixFmt) { NSLog(@"No Accelerated OpenGL pixel format found\n"); NSOpenGLPixelFormatAttribute attrs2[] = { NSOpenGLPFANoRecovery, 0 }; // Get pixel format from OpenGL pixFmt = [[NSOpenGLPixelFormat alloc] initWithAttributes:attrs2]; if (!pixFmt) { NSLog(@"No OpenGL pixel format found!\n"); [self release]; return nil; } } [self setPixelFormat:[pixFmt autorelease]]; /* long swapInterval = 1 ; [[self openGLContext] setValues:&swapInterval forParameter:NSOpenGLCPSwapInterval]; */ [glLock lock]; [[self openGLContext] makeCurrentContext]; // Init object members strExt = glGetString (GL_EXTENSIONS); texture_range = gluCheckExtension ((const unsigned char *)"GL_APPLE_texture_range", strExt) ? GL_TRUE : GL_FALSE; texture_hint = GL_STORAGE_SHARED_APPLE ; client_storage = gluCheckExtension ((const unsigned char *)"GL_APPLE_client_storage", strExt) ? GL_TRUE : GL_FALSE; rect_texture = gluCheckExtension((const unsigned char *)"GL_EXT_texture_rectangle", strExt) ? GL_TRUE : GL_FALSE; // Setup some basic OpenGL stuff glPixelStorei(GL_UNPACK_ALIGNMENT, 1); glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_REPLACE); glColor4f(1.0f, 1.0f, 1.0f, 1.0f); glClearColor(0.0f, 0.0f, 0.0f, 1.0f); glClear(GL_COLOR_BUFFER_BIT); // Loads the shaders shader=LoadShader(GL_FRAGMENT_SHADER,"/Users/alexandremathieu/fragment.fs"); program=glCreateProgram(); glAttachShader(program, shader); glLinkProgram(program); glUseProgram(program); [NSOpenGLContext clearCurrentContext]; [glLock unlock]; image_width = 1024; image_height = 512; image_depth = 16; image_type = GL_UNSIGNED_SHORT_1_5_5_5_REV; image_base = (GLubyte *) calloc(((IMAGE_COUNT * image_width * image_height) / 3) * 4, image_depth >> 3); if (image_base == nil) { [self release]; return nil; } // Create and load textures for the first time [self loadTextures:GL_TRUE]; // Init fps timer //gettimeofday(&cycle_time, NULL); drawBG = YES; // Call for a redisplay noDisplay = YES; PSXDisplay.Disabled = 1; [self setNeedsDisplay:true]; return self; } And here is the "render screen" function wich basically...renders the screen. - (void)renderScreen { int bufferIndex = whichImage; glBindTexture(GL_TEXTURE_RECTANGLE_EXT, bufferIndex+1); glUseProgram(program); int loc=glGetUniformLocation(program, "texture"); glUniform1i(loc,bufferIndex+1); glTexSubImage2D(GL_TEXTURE_RECTANGLE_EXT, 0, 0, 0, image_width, image_height, GL_BGRA, image_type, image[bufferIndex]); glBegin(GL_QUADS); glTexCoord2f(0.0f, 0.0f); glVertex2f(-1.0f, 1.0f); glTexCoord2f(0.0f, image_height); glVertex2f(-1.0f, -1.0f); glTexCoord2f(image_width, image_height); glVertex2f(1.0f, -1.0f); glTexCoord2f(image_width, 0.0f); glVertex2f(1.0f, 1.0f); glEnd(); [[self openGLContext] flushBuffer]; [NSOpenGLContext clearCurrentContext]; //[glLock unlock]; } and finally here's the shader. uniform sampler2DRect texture; void main() { vec4 color, texel; color = gl_Color; texel = texture2DRect(texture, gl_TexCoord[0].xy); color *= texel; // Begin Shader float gray=0.0; gray+=(color.r + color.g + color.b)/3.0; color=vec4(gray,gray,gray,color.a); // End Shader gl_FragColor = color; } The loading and using of shaders works since I am able to turn the screen all red with this shader void main(){ gl_FragColor=vec4(1.0,0.0,0.0,1.0); } If the shader contains a syntax error I get an error message from the LoadShader function etc. If I remove the use of the shader, everything works normally. I think the problem comes from the "passing the texture as a uniform parameter" thing. But these are my very firsts step with openGL and I cant be sure of anything. Don't hesitate to ask for more info. Thank you Stack O.

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