Iphone – OpenGL to OpenGL-ES – glBegin();

iphoneopengl-es

I am trying to learn to write OpenGL apps for the iPhone. How can I port the following code to work with OpenGL-ES? I know that I must store the vertices in an array and then call glDrawArrays(), but is there an optimal way to do this? My thought is to create a very large array and simply keep a counter of how many spaces are filled. This there a better approach? What about using an NSArray and then converting back to a c array?

glBegin(GL_LINE_STRIP);

z = -50.0f;
for(angle = 0.0f; angle <= (2.0f*3.1415f)*3.0f; angle += 0.1f)
    {
    x = 50.0f*sin(angle);
    y = 50.0f*cos(angle);

    // Specify the point and move the Z value up a little   
    glVertex3f(x, y, z);
    z += 0.5f;
    }

// Done drawing points
glEnd();

Best Solution

If you have sufficient space and know the maximum size of the array, it's simplest to use one big statically allocated array and just keep track of its current logical size.

If memory is scant but processor resources are plentiful then pack the array on the fly and then register the arrays and call glDrawArrays().

The hybrid approach would be to use a dynamically allocated array that can be updated (if necessary). You can do this manually by reallocating a dynamic array when it approaches becoming full or by using an NSMutableArray of some sort. (N.B. NSArray is for static arrays; NSMutableArrays (subclass) are dynamic. See here.)

Hope this helped :)

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Android – Draw text in OpenGL ES

Rendering text to a texture is simpler than what the Sprite Text demo make it looks like, the basic idea is to use the Canvas class to render to a Bitmap and then pass the Bitmap to an OpenGL texture:

// Create an empty, mutable bitmap
Bitmap bitmap = Bitmap.createBitmap(256, 256, Bitmap.Config.ARGB_4444);
// get a canvas to paint over the bitmap
Canvas canvas = new Canvas(bitmap);
bitmap.eraseColor(0);

// get a background image from resources
// note the image format must match the bitmap format
Drawable background = context.getResources().getDrawable(R.drawable.background);
background.setBounds(0, 0, 256, 256);
background.draw(canvas); // draw the background to our bitmap

// Draw the text
Paint textPaint = new Paint();
textPaint.setTextSize(32);
textPaint.setAntiAlias(true);
textPaint.setARGB(0xff, 0x00, 0x00, 0x00);
// draw the text centered
canvas.drawText("Hello World", 16,112, textPaint);

//Generate one texture pointer...
gl.glGenTextures(1, textures, 0);
//...and bind it to our array
gl.glBindTexture(GL10.GL_TEXTURE_2D, textures[0]);

//Create Nearest Filtered Texture
gl.glTexParameterf(GL10.GL_TEXTURE_2D, GL10.GL_TEXTURE_MIN_FILTER, GL10.GL_NEAREST);
gl.glTexParameterf(GL10.GL_TEXTURE_2D, GL10.GL_TEXTURE_MAG_FILTER, GL10.GL_LINEAR);

//Different possible texture parameters, e.g. GL10.GL_CLAMP_TO_EDGE
gl.glTexParameterf(GL10.GL_TEXTURE_2D, GL10.GL_TEXTURE_WRAP_S, GL10.GL_REPEAT);
gl.glTexParameterf(GL10.GL_TEXTURE_2D, GL10.GL_TEXTURE_WRAP_T, GL10.GL_REPEAT);

//Use the Android GLUtils to specify a two-dimensional texture image from our bitmap
GLUtils.texImage2D(GL10.GL_TEXTURE_2D, 0, bitmap, 0);

//Clean up
bitmap.recycle();

OpenGL ES versus OpenGL

Two of the more significant differences between OpenGL ES and OpenGL are the removal of the glBegin ... glEnd calling semantics for primitive rendering (in favor of vertex arrays) and the introduction of fixed-point data types for vertex coordinates and attributes to better support the computational abilities of embedded processors, which often lack an FPU

Have a look here: OpenGL_ES

Best Solution

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Android – Draw text in OpenGL ES

OpenGL ES versus OpenGL

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