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SDL Opengl mode 2D Texture Mapping

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Started by maxfire January 30, 2012 09:54 AM

1 comment, last by maxfire 12 years, 2 months ago

maxfire

210

Author

January 30, 2012 09:54 AM

Hi guys' im having a few problems with clipping a 2D texture in SDL OpenGL mode.

Currently I have the image clipping but when it blends to the screen it distorts/twists ( I'll just put a screen shot up

). Now I know its something to do with my Quad matrix but I just can't see the error. Here's my function any advice would be great

void MainWnd::RenderSprite( GraphicsTexture* graphic, SDL_Rect position, SDL_Rect clipping )

{

		glColor4ub( 255,255,255,255 );



glEnable( GL_TEXTURE_2D );



glBindTexture( GL_TEXTURE_2D, graphic->GetTexture() );



glTranslatef( position.x, position.y, 0 );



float x = 0;

float y = 0;



	glBegin( GL_QUADS );



x = GetClippingPercentage( clipping.x, clipping.w );

y = GetClippingPercentage( clipping.y, clipping.h );



glTexCoord2d( x, y );

glVertex3f( 0.0, 0.0, 0.0 );//top left



x = GetClippingPercentage( ( clipping.x + clipping.w ), graphic->_TextureDimentions.width );

y = GetClippingPercentage( clipping.y, graphic->_TextureDimentions.height );



glTexCoord2d( x, y );

glVertex3f( ( position.w + 0.0 ), 0.0, 0.0 );//top right



x = GetClippingPercentage( clipping.w + 0.0, graphic->_TextureDimentions.width + 0.0 );

y = GetClippingPercentage( ( clipping.y + clipping.h + 0.0 ), ( graphic->_TextureDimentions.height + 0.0 ) );



glTexCoord2d( x, y );

glVertex3f( ( position.w + 0.0 ), ( position.h + 0.0 ), 0.0 );//bottom right



x = GetClippingPercentage( clipping.x + 0.0 , graphic->_TextureDimentions.width + 0.0 );

y = GetClippingPercentage( clipping.h + 0.0, graphic->_TextureDimentions.height + 0.0 );



glTexCoord2d( x, y );

glVertex3f( 0.0, ( position.h + 0.0 ), 0.0 );//bottom left



glEnd();



glDisable( GL_TEXTURE_2D );



//Reset

	glLoadIdentity();

}

float MainWnd::GetClippingPercentage( int inner, int outer )

{

float value = ( float ) ( inner ) / ( float ) ( outer + 0.0 );

return value;

}

Update: I worked out by hand the clipping margins ( multiplying the float value by the texture size and the outcomes match the clipping rect ) so the math is correct. Am I missing something?

SimonForsman

7,644

January 30, 2012 06:33 PM

Try glScissor: http://www.opengl.or...l/glScissor.xml

glScissor is probably the easiest way to do clipping.



void MainWnd::RenderSprite( GraphicsTexture* graphic, SDL_Rect position, SDL_Rect clipping ) {

		glColor4ub( 255,255,255,255 );

		glEnable(GL_SCISSOR_TEST);

		glEnable( GL_TEXTURE_2D );

		glBindTexture( GL_TEXTURE_2D, graphic->GetTexture() );

		glLoadIdentity();

		glTranslatef( position.x, position.y, 0 );

		glScissor(clipping.x,clipping.y,clipping.w,clipping.h);



		glBegin(GL_QUADS);

		glTextCoord2(0.0f,0.0f); glVertex3f(0.0f,0.0f,0.0f);

		glTextCoord2(1.0f,0.0f); glVertex3f((float)position.w,0.0f,0.0f);

		glTextCoord2(1.0f,1.0f); glVertex3f((float)position.w,float(position.h,0.0f);

		glTextCoord2(0.0f,1.0f); glVertex3f(0.0f,position.h,0.0f);

		glEnd();

		glDisable(GL_SCISSOR_TEST);

}