Drawable2d.cs

using System;
using Java.Nio;

namespace Grafika.GLES
{
    public class Drawable2d
    {
        private static int SIZEOF_FLOAT = 4;

        /**
         * Simple equilateral triangle (1.0 per side).  Centered on (0,0).
         */
        private static float[] TRIANGLE_COORDS = {
             0.0f,  0.577350269f,   // 0 top
            -0.5f, -0.288675135f,   // 1 bottom left
             0.5f, -0.288675135f    // 2 bottom right
        };
        private static float[] TRIANGLE_TEX_COORDS = {
            0.5f, 0.0f,     // 0 top center
            0.0f, 1.0f,     // 1 bottom left
            1.0f, 1.0f,     // 2 bottom right
        };
        private static FloatBuffer TRIANGLE_BUF =
            GlUtil.createFloatBuffer(TRIANGLE_COORDS);
        private static FloatBuffer TRIANGLE_TEX_BUF =
            GlUtil.createFloatBuffer(TRIANGLE_TEX_COORDS);

        /**
         * Simple square, specified as a triangle strip.  The square is centered on (0,0) and has
         * a size of 1x1.
         * <p>
         * Triangles are 0-1-2 and 2-1-3 (counter-clockwise winding).
         */
        private static float[] RECTANGLE_COORDS = {
            -0.5f, -0.5f,   // 0 bottom left
             0.5f, -0.5f,   // 1 bottom right
            -0.5f,  0.5f,   // 2 top left
             0.5f,  0.5f,   // 3 top right
        };
        private static float[] RECTANGLE_TEX_COORDS = {
            0.0f, 1.0f,     // 0 bottom left
            1.0f, 1.0f,     // 1 bottom right
            0.0f, 0.0f,     // 2 top left
            1.0f, 0.0f      // 3 top right
        };
        private static FloatBuffer RECTANGLE_BUF =
            GlUtil.createFloatBuffer(RECTANGLE_COORDS);
        private static FloatBuffer RECTANGLE_TEX_BUF =
            GlUtil.createFloatBuffer(RECTANGLE_TEX_COORDS);

        /**
         * A "full" square, extending from -1 to +1 in both dimensions.  When the model/view/projection
         * matrix is identity, this will exactly cover the viewport.
         * <p>
         * The texture coordinates are Y-inverted relative to RECTANGLE.  (This seems to work out
         * right with external textures from SurfaceTexture.)
         */
        private static float[] FULL_RECTANGLE_COORDS = {
            -1.0f, -1.0f,   // 0 bottom left
             1.0f, -1.0f,   // 1 bottom right
            -1.0f,  1.0f,   // 2 top left
             1.0f,  1.0f,   // 3 top right
        };
            private static float[] FULL_RECTANGLE_TEX_COORDS = {
            0.0f, 0.0f,     // 0 bottom left
            1.0f, 0.0f,     // 1 bottom right
            0.0f, 1.0f,     // 2 top left
            1.0f, 1.0f      // 3 top right
        };
        private static FloatBuffer FULL_RECTANGLE_BUF =
            GlUtil.createFloatBuffer(FULL_RECTANGLE_COORDS);
        private static FloatBuffer FULL_RECTANGLE_TEX_BUF =
            GlUtil.createFloatBuffer(FULL_RECTANGLE_TEX_COORDS);


        private FloatBuffer mVertexArray;
            private FloatBuffer mTexCoordArray;
            private int mVertexCount;
            private int mCoordsPerVertex;
            private int mVertexStride;
            private int mTexCoordStride;
            private Prefab mPrefab;

        /**
         * Enum values for constructor.
         */
        public enum Prefab
        {
            TRIANGLE, RECTANGLE, FULL_RECTANGLE
        }

        /**
         * Prepares a drawable from a "pre-fabricated" shape definition.
         * <p>
         * Does no EGL/GL operations, so this can be done at any time.
         */
        public Drawable2d(Prefab shape)
        {
            switch (shape)
            {
                case Prefab.TRIANGLE:
                    mVertexArray = TRIANGLE_BUF;
                    mTexCoordArray = TRIANGLE_TEX_BUF;
                    mCoordsPerVertex = 2;
                    mVertexStride = mCoordsPerVertex * SIZEOF_FLOAT;
                    mVertexCount = TRIANGLE_COORDS.Length / mCoordsPerVertex;
                    break;
                case Prefab.RECTANGLE:
                    mVertexArray = RECTANGLE_BUF;
                    mTexCoordArray = RECTANGLE_TEX_BUF;
                    mCoordsPerVertex = 2;
                    mVertexStride = mCoordsPerVertex * SIZEOF_FLOAT;
                    mVertexCount = RECTANGLE_COORDS.Length / mCoordsPerVertex;
                    break;
                case Prefab.FULL_RECTANGLE:
                    mVertexArray = FULL_RECTANGLE_BUF;
                    mTexCoordArray = FULL_RECTANGLE_TEX_BUF;
                    mCoordsPerVertex = 2;
                    mVertexStride = mCoordsPerVertex * SIZEOF_FLOAT;
                    mVertexCount = FULL_RECTANGLE_COORDS.Length / mCoordsPerVertex;
                    break;
                default:
                    throw new Exception("Unknown shape " + shape);
            }
            mTexCoordStride = 2 * SIZEOF_FLOAT;
            mPrefab = shape;
        }

        /**
         * Returns the array of vertices.
         * <p>
         * To avoid allocations, this returns internal state.  The caller must not modify it.
         */
        public FloatBuffer getVertexArray()
        {
            return mVertexArray;
        }

        /**
         * Returns the array of texture coordinates.
         * <p>
         * To avoid allocations, this returns internal state.  The caller must not modify it.
         */
        public FloatBuffer getTexCoordArray()
        {
            return mTexCoordArray;
        }

        /**
         * Returns the number of vertices stored in the vertex array.
         */
        public int getVertexCount()
        {
            return mVertexCount;
        }

        /**
         * Returns the width, in bytes, of the data for each vertex.
         */
        public int getVertexStride()
        {
            return mVertexStride;
        }

        /**
         * Returns the width, in bytes, of the data for each texture coordinate.
         */
        public int getTexCoordStride()
        {
            return mTexCoordStride;
        }

        /**
         * Returns the number of position coordinates per vertex.  This will be 2 or 3.
         */
        public int getCoordsPerVertex()
        {
            return mCoordsPerVertex;
        }
    }
}