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QuestionDrawing a simple triangle horror when using std::vector Pin
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QuestionLooking for a C# option for doing simple 2D graphics Pin
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QuestionSharpDX MediaFoundation and DirectShow Pin
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QuestionPygame image wont show up until I close the window Pin
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QuestionOpenGL stencil in 2D - advanced (?) issues Pin
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QuestionOpenGL removing "objects" - how ? Pin
Vaclav_9-Apr-20 9:53
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AnswerRe: OpenGL removing "objects" - how ? Pin
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GeneralRe: OpenGL removing "objects" - how ? Pin
Vaclav_10-Apr-20 5:35
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As a general "rule" NOT to invite uncalled for criticism on my under construction code I am therefore very reluctant to post code.
However, every rule has an exception so here is the latest implementation of "write text message" to OpenGL window.
It writes the message, but in wrong position - irrelevant for now.
(The disabled #ifdef / #endif code was added and that is why the message is written in wrong raster position.The raster position code must be in wrong place. )
It is my understanding that OpenGL keeps the data - bitmap in this case - in video card hardware. So to override / update the data I have to access that particular hardware .
Or in another words - OpenGL "variable / object" cannot be just overwritten like C code.

So I believe I need to keep track of "matrix" where the initial bitmap is written and then
glLoadIdentity();
should clear the entire matrix.

Correct me if I am wrong, but glClear would not work SELECTIVELY , it would clear entire buffer.( I did neglected to add "selectively" to the post title )



C++
<pre>//display
// normal parametrized function
// passive
void OpenGL_text(char *message, float x, float y, float z) {

//#ifdef BYPASS
	printf("\nOPENGL TRACE OpenGL  @function %s  @line %i \n", __FUNCTION__,
	__LINE__);

	printf("\nOPENGL TRACE STOP passed message %s @line %i\n", message,
	__LINE__);
//#endif passive

	char menu[80];
	strcpy(menu, message); // local copy ??
	int len;
	len = strlen(menu);
	glColor3f(1, 1, 1);    // white text

//#ifdef BYPASS
	{ // GL_PROJECTION block
		glMatrixMode( GL_PROJECTION); // ??
		glPushMatrix();               // there is only one (?)
		glLoadIdentity();             // clear projection matrix  - why (?)

		gluOrtho2D(0, 500, 0, 500);   // MN !!
		{ // GL_MODELVIEW block
			glMatrixMode( GL_MODELVIEW);
			glPushMatrix();

			glLoadIdentity();         // clear bitmap (?)
//#endif
			glRasterPos3f(x, y, z); // wrong !! text start postion

			for (int i = 0; i < len; ++i) {
				glutBitmapCharacter(GLUT_BITMAP_HELVETICA_18, menu[i]);
			}
//#ifdef BYPASS
			glPopMatrix();        // GL_MODELVIEW
		} // GL_MODELVIEW block
		glMatrixMode( GL_PROJECTION);
		glPopMatrix();
	} // GL_PROJECTION block
	glMatrixMode( GL_MODELVIEW);
//#endif

}


GeneralRe: OpenGL removing "objects" - how ? Pin
Graham Breach10-Apr-20 6:45
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GeneralSOLVED Re: OpenGL removing "objects" - how ? Pin
Vaclav_10-Apr-20 7:08
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GeneralRe: OpenGL removing "objects" - how ? Pin
jhonaa22-Mar-22 1:23
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