CODEWITHSUNDEEP
opengl
david
david

Reputation: 292

OpenGL faded square

I'm trying to achieve a fade effect, where the corners of a square have different alphas. I'm doing this:

glBegin(GL_QUADS);

glColor4d(r, g, b, alphaTopLeft);
glVertex2d(x, y);
glColor4d(r, g, b, alphaTopRight);
glVertex2d(x + width, y);
glColor4d(r, g, b, alphaBottomRight);
glVertex2d(x + width, y + height);
glColor4d(r, g, b, alphaBottomLeft);
glVertex2d(x, y + height);

glEnd();

With the values alphaTopLeft = 0, alphaTopRight = 0, alphaBottomRight = 1, alphaBottomLeft = 1, but it produces a solid shape (all corners alpha 1), why?

Upvotes: 1

Views: 65

Answers (1)

Dan
Dan

Reputation: 1486

Have you enabled GL_BLEND? Try adding this before you render: 

glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA); 
glEnable( GL_BLEND );

Upvotes: 3

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