// C function void glDrawArrays ( GLenum mode, GLint first, GLsizei count ) public static native void glDrawArrays( int mode, int first, int count );
mode:可以有如下选项
public static final int GL_POINTS = 0x0000;//点
public static final int GL_LINES = 0x0001;//线
public static final int GL_LINE_LOOP = 0x0002;//线段
public static final int GL_LINE_STRIP = 0x0003;
public static final int GL_TRIANGLES = 0x0004;
public static final int GL_TRIANGLE_STRIP = 0x0005;
public static final int GL_TRIANGLE_FAN = 0x0006;
first:从数组第几个开始
count:绘制的点数。
下面逐一实验这些mode
一、GL_POINTS
package com.tian.studyopengles.points import android.opengl.GLES20 import android.opengl.GLSurfaceView import com.tian.studyopengles.utils.GL2Utils import javax.microedition.khronos.egl.EGLConfig import javax.microedition.khronos.opengles.GL10 class OnePointsRender : GLSurfaceView.Renderer { private val V_SHADER_SOURCE = "" + "void main(){\n" + "gl_Position = vec4(0.0,0.0,0.0,1.0);\n" + "gl_PointSize = 10.0;\n" + "}" private val F_SHADER_SOURCE = "" + "void main(){\n" + "gl_FragColor = vec4(1.0,0.0,0.0,1.0);" + "}" private var mProgram: Int = -1 override fun onDrawFrame(gl: GL10?) { GLES20.glClearColor(0.0f, 0.0f, 0.0f, 1.0f) GLES20.glClear(GLES20.GL_COLOR_BUFFER_BIT) GLES20.glDrawArrays(GLES20.GL_POINTS, 0, 1) } override fun onSurfaceChanged(gl: GL10?, width: Int, height: Int) { GLES20.glViewport(0, 0, width, height) } override fun onSurfaceCreated(gl: GL10?, config: EGLConfig?) { GLES20.glClearColor(0.0f, 0.0f, 0.0f, 1.0f) mProgram = GL2Utils.createProgram(V_SHADER_SOURCE, F_SHADER_SOURCE) GLES20.glUseProgram(mProgram) } }
这是最简单的,绘制一个固定的点。
如何绘制多个点?
package com.tian.studyopengles.points import android.opengl.GLES20 import android.opengl.GLSurfaceView import com.tian.studyopengles.utils.GL2Utils import com.tian.studyopengles.utils.LogUtils import java.nio.ByteBuffer import java.nio.ByteOrder import javax.microedition.khronos.egl.EGLConfig import javax.microedition.khronos.opengles.GL10 class MultiplePointsRender : GLSurfaceView.Renderer { private val V_SHADER_SOURCE = "" + "attribute vec4 a_Position;\n" + "void main(){\n" + "gl_Position = a_Position;\n" + "gl_PointSize = 20.0;\n" + "}" private val F_SHADER_SOURCE = "" + "void main(){\n" + "gl_FragColor = vec4(1.0,0.0,0.0,1.0);\n" + "}" private val vertexPoints = floatArrayOf( 0.0f, 0.0f, -0.5f, -0.5f, 0.5f, 0.5f ) private var mProgram: Int = -1 override fun onDrawFrame(gl: GL10?) { GLES20.glClearColor(0.0f, 0.0f, 0.0f, 1.0f) GLES20.glClear(GLES20.GL_COLOR_BUFFER_BIT) GLES20.glDrawArrays(GLES20.GL_POINTS, 0, 3) } override fun onSurfaceChanged(gl: GL10?, width: Int, height: Int) { GLES20.glViewport(0, 0, width, height) } override fun onSurfaceCreated(gl: GL10?, config: EGLConfig?) { mProgram = GL2Utils.createProgram(V_SHADER_SOURCE, F_SHADER_SOURCE) val buffer = ByteBuffer.allocateDirect(vertexPoints.size * 4) .order(ByteOrder.nativeOrder()) .asFloatBuffer() .put(vertexPoints) .position(0) val position = GLES20.glGetAttribLocation(mProgram, "a_Position") GLES20.glVertexAttribPointer(position, 2, GLES20.GL_FLOAT, false, 0, buffer) GLES20.glEnableVertexAttribArray(position) GLES20.glValidateProgram(mProgram) val statusArray = IntArray(1) GLES20.glGetProgramiv(mProgram, GLES20.GL_VALIDATE_STATUS, statusArray, 0) val statusInfo = GLES20.glGetProgramInfoLog(mProgram) LogUtils.i("status code == ${statusArray[0]},status info == $statusInfo") GLES20.glUseProgram(mProgram) } }
注意的点:1、shader不要写错,代码里面有工具方法,可以监测出是否出错。
2、因为是平面绘制,只用了(x,y)表示坐标,shader里面定义的是vec4 表示四个向量,此次表示默认第三和第四是(0.0,1.0)。
GLES20.glVertexAttribPointer(position, 2, GLES20.GL_FLOAT, false, 0, buffer)中的2,表示是几个数据来表示一个顶点坐标。此处是(x,y)则所以是2
3、这三行,铁三角,先定位、再赋值、最后激活。
val position = GLES20.glGetAttribLocation(mProgram, "a_Position")
GLES20.glVertexAttribPointer(position, 2, GLES20.GL_FLOAT, false, 0, buffer)
GLES20.glEnableVertexAttribArray(position)