CODEWITHSUNDEEP
androidopengl-esopengl-es-2.0
user7904027
user7904027

Reputation:

Is glClear(GL_COLOR_BUFFER_BIT) necessary when I already glDisable(GL_BLEND)?

In my understanding, if I disable GL_BLEND, then no blending happens at all. So I don't need do glClear(GL_COLOR_BUFFER_BIT).

I am working on GLES20 for Android programming. I have added the line below.

GLES20.glDisable(GLES20.GL_BLEND);

If I don't add glClear(GL_COLOR_BUFFER_BIT), all other devices work well except Nexus 4. On Nexus 4, on one pass (other passes work normally), only partial area is rendered. If I add glClear(GL_COLOR_BUFFER_BIT), then now Nexus 4 works well.

Upvotes: 0

Views: 1089

Answers (1)

Rabbid76
Rabbid76

Reputation: 211228

If GL_BLEND is disabled, then a fragment of the draw buffer will be overwritten, if it is drawn to.
If you disable blending and you write on every fragment of the draw buffer in every frame, then it is useless to clear the draw buffer, because each fragment will be set during the drawing process.
glClear(GL_COLOR_BUFFER_BIT) does nothing else than to write to every fragment with a constant color set by glClearColor.

Note, you have to ensure, that every fragment is written in each frame. For example if GL_DEPTH_TEST is enabled you'll have to glClear(GL_DEPTH_BUFFER_BIT anyway.

Upvotes: 1

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