Question about glBindTexture

Question

This is a method I use to draw sprites:

public void DrawSprite(Sprite sprite)
        {
            Gl.glBegin(Gl.GL_TRIANGLES);
            {
                for (int i = 0; i < Sprite.VertexAmount; i++)
                {
                    Gl.glBindTexture(Gl.GL_TEXTURE_2D, sprite.Texture.Id);
                    DrawImmediateModeVertex(
                    sprite.VertexPositions[i],
                    sprite.VertexColors[i],
                    sprite.VertexUVs[i]);
                }
            }
            Gl.glEnd();
        }

DrawImmediateModeVertex - draws one vertex.

Should I get Gl.glBindTexture out of the for loop? Also strange things happen when I render a texture, even though i provide sprites with different texture ids, just one same texture is drawn every time.

score 6 · Answer 1 · answered Aug 11 '11 at 07:17

6

From OpenGL documentation:

GL_INVALID_OPERATION is generated if glBindTexture is executed between the execution of glBegin and the corresponding execution of glEnd.

You should extract glBindTexture outside glBegin...glEnd pair

answered Aug 11 '11 at 07:17

Mihai Maruseac

20,967
7
57
109

1

This, and you should preferrably not bind a new texture for every sprite _at all_ anyway. Binding textures requires non-trivial work in the driver, and while vertex-per-vertex immediate mode already is not terribly high-performance, thousands of texture binds additionally kill performance. Sorting sprites by texture would be the correct thing to do, but even caching the texture identifier in a variable and only binding if the last known value is not the current one would already be better. – Damon Aug 11 '11 at 09:48

score 0 · Answer 2 · answered Aug 11 '11 at 07:16

0

Yes, move the bind outside of the loop, no need to repeatedly bind the same texture.

answered Aug 11 '11 at 07:16

Jet

59
5

Question about glBindTexture

2 Answers2