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copied!<p>If I understand you correctly then this should be close to what you after, using glReadPixels and glDrawPixels.</p> <p><a href="http://img392.imageshack.us/img392/8540/zoomla1.jpg" rel="nofollow noreferrer"></a></p> <p>Sorry it's C++ not C# but the OpenGL function should still be the same.</p> <pre><code>// main.cpp // glut Text #ifdef __WIN32__ #define WIN32_LEAN_AND_MEAN #include <windows.h> #endif #include <GL/glut.h> #include <cstdio> int WIDTH = 800; int HEIGHT = 600; int MouseButton, MouseY = 0, MouseX = 0; const int size = 80; char *image, rect[size*size*3]; int imagewidth, imageheight; bool Init() { int offset; FILE* file = fopen("image.bmp", "rb"); if (file == NULL) return false; fseek(file, 10, SEEK_SET); fread(&offset, sizeof(int), 1, file); fseek(file, 18, SEEK_SET); fread(&imagewidth, sizeof(int), 1, file); fread(&imageheight, sizeof(int), 1, file); fseek(file, offset, SEEK_SET); image = new char[imagewidth*imageheight*3]; if (image == NULL) return false; fread(image, 1, imagewidth*imageheight*3, file); fclose(file); return true; } void Reshape(int width, int height) { WIDTH = width; HEIGHT = height; glViewport(0 , 0, width, height); glMatrixMode(GL_PROJECTION); glLoadIdentity(); gluOrtho2D(0, width, 0, height); } void Display() { int size2 = size/2; glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); glMatrixMode(GL_MODELVIEW); glLoadIdentity(); glRasterPos2i(0,0); glPixelZoom(1.f, 1.f); glDrawPixels(imagewidth, imageheight, 0x80E0/*GL_RGB*/, GL_UNSIGNED_BYTE, image); glReadPixels(MouseX-size2, MouseY-size2, size, size, GL_RGB, GL_UNSIGNED_BYTE, rect); glPixelZoom(2.f, 2.f); glRasterPos2i(MouseX-size, MouseY-size); glDrawPixels(size, size, GL_RGB, GL_UNSIGNED_BYTE, rect); glFlush(); glutSwapBuffers(); } void Mouse(int button, int state, int x, int y) { if (state == GLUT_DOWN) MouseButton &= (1<<button); else MouseButton &= ~(1<<button); } void MouseMove(int x, int y) { MouseX = x; MouseY = HEIGHT - y; } int main(int argc, char* argv[]) { glutInit(&argc, argv); if (Init() == false) return 1; glutInitWindowSize(WIDTH, HEIGHT); glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGBA); glutCreateWindow("glut_Text"); glClearColor(0.25, 0.25, 0.25, 1.0); glutReshapeFunc(Reshape); glutDisplayFunc(Display); glutIdleFunc(Display); glutMouseFunc(Mouse); glutMotionFunc(MouseMove); glutPassiveMotionFunc(MouseMove); glutMainLoop(); return 0; } </code></pre> <p>Hope this helps.</p>

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