My question is quite trivial I believe, I'm using OpenGL ES 2.0 to draw a simple 2D scene.
I have a background texture that stretches the whole screen and another texture of a flower (or shel I say sprite?) that drawn at a specific location on screen.
So the trivial why i can think of doing it is to call glDrawArrays
twice, one with the vertices of the background texture, and another one with the vertices of the flower texture.
Is that the right way? if so, is that mean that for 10 flowers i'll need to call glDrawArrays
10 times?
And what about blending? what if i want to blend the flower with the background, i need both the background and flower pixel colors and that may be a problem with two draws no?
Or is it possible to do it in one draw? if so how can I create a shader that knows if it now processing the background texture vertex or the flower texture vertex?
Or is it possible to do it in one draw?
The problem with one draw is that the shader needs to know if the current vertex is a background vertex (than use the background texture color) or a flower vertex( than use the flower texture color), and I don't know how to do it.
Here is how I use one draw call to draw the background image stretches the whole screen and the flower is half size centered.
- (void)renderOnce {
//... set program, clear color..
glActiveTexture(GL_TEXTURE2);
glBindTexture(GL_TEXTURE_2D, backgroundTexture);
glUniform1i(backgroundTextureUniform, 2);
glActiveTexture(GL_TEXTURE3);
glBindTexture(GL_TEXTURE_2D, flowerTexture);
glUniform1i(flowerTextureUniform, 3);
static const GLfloat allVertices[] = {
-1.0f, -1.0f, // background texture coordinates
1.0f, -1.0f, // to draw in whole screen
-1.0f, 1.0f, //
1.0f, 1.0f,
-0.5f, -0.5f, // flower texture coordinates
0.5f, -0.5f, // to draw half screen size
-0.5f, 0.5f, // and centered
0.5f, 0.5f, //
};
// both background and flower texture coords use the whole texture
static const GLfloat backgroundTextureCoordinates[] = {
0.0f, 0.0f,
1.0f, 0.0f,
0.0f, 1.0f,
1.0f, 1.0f,
};
static const GLfloat flowerTextureCoordinates[] = {
0.0f, 0.0f,
1.0f, 0.0f,
0.0f, 1.0f,
1.0f, 1.0f,
};
glVertexAttribPointer(positionAttribute, 2, GL_FLOAT, 0, 0, allVertices);
glVertexAttribPointer(backgroundTextureCoordinateAttribute, 2, GL_FLOAT, 0, 0, backgroundTextureCoordinates);
glVertexAttribPointer(flowerTextureCoordinateAttribute, 2, GL_FLOAT, 0, 0, flowerTextureCoordinates);
glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
}
A texture is an OpenGL Object that contains one or more images that all have the same image format. A texture can be used in two ways: it can be the source of a texture access from a Shader, or it can be used as a render target.
The OpenGL ES 3.0 API provides additional features and better performance than the 2.0 API and is also backward compatible. This means that you can potentially write your application targeting OpenGL ES 2.0 and conditionally include OpenGL ES 3.0 graphics features if they are available.
About the Android Extension Pack AEP is a set of OpenGL ES extensions that bring console-class gaming to Android. AEP features include: ASTC (LDR) texture compression format. Compute shaders. Geometry shaders.
OpenGL 3. x defines the minimum number for the per-stage limit to be 16, so hardware cannot have fewer than 16 textures-per-stage.
You have two choices:
The second way is obviously the better and the right one.To get an idea of how to do it ,look at my awnser here
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