Android 上的 openGl es 在右上角显示一个正方形

Question

我写了一个代码，它应该在屏幕上绘制一个带有颜色渐变的正方形，但由于某种原因，它还在屏幕的右上角绘制了一个蓝色正方形。蓝色方块有时会改变它的颜色，当我更改代码中的内容时，这与它完全无关，例如我的渲染器中的一行代码，我在其中以像素为单位读取屏幕大小。有时当我截屏时它也会消失。这是代码：

import android.content.Context;
import android.opengl.GLES30;
import android.util.Log;

import java.io.BufferedReader;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.nio.ByteBuffer;
import java.nio.ByteOrder;
import java.nio.FloatBuffer;
import java.nio.IntBuffer;


public class Square {
int ShaderProgramID;
private FloatBuffer vertexBuffer;
private int vertexBufferID;
private int vertexCount;
private int vertexStride;
static final int COORDS_PER_VERTEX = 3;
static final int COLORS_PER_VERTEX = 4;
static final int SIZE_OF_FLOAT = 4;
static final float coords[] = {
        //x:    y:     z:            r:    g:    b:    a:
        -0.5f, 0.5f, 0.0f,         1.0f, 0.0f, 0.0f, 1.0f,
        -0.5f,-0.5f, 0.0f,         0.0f, 1.0f, 0.0f, 1.0f,
         0.5f,-0.5f, 0.0f,         0.0f, 0.0f, 1.0f, 1.0f,
        -0.5f, 0.5f, 0.0f,         1.0f, 0.0f, 0.0f, 1.0f,
         0.5f,-0.5f, 0.0f,         0.0f, 1.0f, 0.0f, 1.0f,
         0.5f, 0.5f, 0.0f,         0.0f, 0.0f, 1.0f, 1.0f

};
public Square(Context context)  {
    String vertexShaderSrc = ReadFromfile("defaultVertexShader.glsl", context);
    String fragmentShaderSrc = ReadFromfile("defaultFragmentShader.glsl", context);

    int vertexID = GLES30.glCreateShader(GLES30.GL_VERTEX_SHADER);
    GLES30.glShaderSource(vertexID, vertexShaderSrc);
    GLES30.glCompileShader(vertexID);
    Log.d("Golden", GLES30.glGetShaderInfoLog(vertexID));

    int fragmetID = GLES30.glCreateShader(GLES30.GL_FRAGMENT_SHADER);
    GLES30.glShaderSource(fragmetID, fragmentShaderSrc);
    GLES30.glCompileShader(fragmetID);
    Log.d("Golden", GLES30.glGetShaderInfoLog(fragmetID) );

    ShaderProgramID = GLES30.glCreateProgram();
    GLES30.glAttachShader(ShaderProgramID, vertexID);
    GLES30.glAttachShader(ShaderProgramID, fragmetID);
    GLES30.glBindAttribLocation(ShaderProgramID, 0, "aPos");
    GLES30.glBindAttribLocation(ShaderProgramID, 1, "aColor");
    GLES30.glLinkProgram(ShaderProgramID);

    positionHandle = GLES30.glGetAttribLocation(ShaderProgramID, "aPos");
    colorHandle = GLES30.glGetAttribLocation(ShaderProgramID, "aColor");

    //vertexBuffer = FloatBuffer.allocate(coords.length);
    //vertexBuffer = ByteBuffer.allocate(coords.length*4).asFloatBuffer();
    //vertexBuffer.put(coords);
    //vertexBuffer.position(0);
    ByteBuffer bb = ByteBuffer.allocateDirect(coords.length * 4);
    bb.order(ByteOrder.nativeOrder());
    vertexBuffer = bb.asFloatBuffer();
    vertexBuffer.put(coords);
    vertexBuffer.position(0);

    IntBuffer buffer = IntBuffer.allocate(1);
    GLES30.glGenBuffers(1, buffer);
    vertexBufferID = buffer.get(0);
    GLES30.glBindBuffer(GLES30.GL_ELEMENT_ARRAY_BUFFER, vertexBufferID);
    GLES30.glBufferData(GLES30.GL_ELEMENT_ARRAY_BUFFER, coords.length * 4, vertexBuffer, GLES30.GL_STATIC_DRAW);

    vertexCount = coords.length / (COORDS_PER_VERTEX + COLORS_PER_VERTEX);
    vertexStride = (COORDS_PER_VERTEX + COLORS_PER_VERTEX) * 4;
}
private int positionHandle;
private int colorHandle;
public void draw() {
    GLES30.glUseProgram(ShaderProgramID);

    vertexBuffer.position(0);
    GLES30.glVertexAttribPointer(positionHandle, COORDS_PER_VERTEX, GLES30.GL_FLOAT, false, vertexStride, vertexBuffer);
    GLES30.glEnableVertexAttribArray(positionHandle);


    vertexBuffer.position(3);
    GLES30.glVertexAttribPointer(colorHandle, COLORS_PER_VERTEX, GLES30.GL_FLOAT, false, vertexStride, vertexBuffer);
    GLES30.glEnableVertexAttribArray(colorHandle);


    GLES30.glDrawArrays(GLES30.GL_TRIANGLES, 0, coords.length);
    GLES30.glDisableVertexAttribArray(positionHandle);
    GLES30.glDisableVertexAttribArray(colorHandle);

}

public String ReadFromfile(String fileName, Context context) {
    StringBuilder ReturnString = new StringBuilder();
    InputStream fIn = null;
    InputStreamReader isr = null;
    BufferedReader input = null;
    try {
        fIn = context.getResources().getAssets()
                .open(fileName);
        isr = new InputStreamReader(fIn);
        input = new BufferedReader(isr);
        String line = "";
        while ((line = input.readLine()) != null) {
            ReturnString.append(line + "\n");
        }
    } catch (Exception e) {
        e.getMessage();
    } finally {
        try {
            if (isr != null)
                isr.close();
            if (fIn != null)
                fIn.close();
            if (input != null)
                input.close();
        } catch (Exception e2) {
            e2.getMessage();
        }
    }
    return ReturnString.toString();
}
}

片段着色器：

#version 300 es
precision mediump float;
in vec4 vColor;
out vec4 oColor;
void main()
{
oColor = vColor;
}

顶点着色器：

#version 300 es
in vec3 aPos;
in vec4 aColor;
out vec4 vColor;

void main()
{
vColor = aColor;
gl_Position = vec4(aPos,1.0);
}

Answer 1

您必须将顶点绑定到 GL_ARRAY_BUFFER 目标而不是 GL_ELEMENT_ARRAY_BUFFER 目标：

IntBuffer buffer = IntBuffer.allocate(1);
GLES30.glGenBuffers(1, buffer);
vertexBufferID = buffer.get(0);
GLES30.glBindBuffer(GLES30.GL_ARRAY_BUFFER, vertexBufferID);
GLES30.glBufferData(GLES30.GL_ARRAY_BUFFER, coords.length * 4, vertexBuffer, GLES30.GL_STATIC_DRAW);

见glVertexAttribPointer:

If a non-zero named buffer object is bound to the GL_ARRAY_BUFFER target (see glBindBuffer), pointer is treated as a byte offset into the buffer object's data store.

在你的例子中 stride 是 28 个字节 ((3+4) * 4)。顶点的offset为0字节，颜色属性的offset为12字节（3 * 4):

GLES30.glBindBuffer(GLES30.GL_ARRAY_BUFFER, vertexBufferID);

GLES30.glVertexAttribPointer(positionHandle, COORDS_PER_VERTEX, 
    GLES30.GL_FLOAT, false, 7*4, 0);
GLES30.glVertexAttribPointer(colorHandle, COLORS_PER_VERTEX, 
    GLES30.GL_FLOAT, false, 7*4, 3*4);

GLES30.glEnableVertexAttribArray(positionHandle);
GLES30.glEnableVertexAttribArray(colorHandle);

glDrawArrays的最后一个参数是顶点数，不是数组中浮点数：

~~GLES30.glDrawArrays(GLES30.GL_TRIANGLES, 0, coords.length / 7);~~

GLES30.glDrawArrays(GLES30.GL_TRIANGLES, 0, coords.length / 7);

Answer 2

在 glDrawArrays 中必须有要绘制的顶点数，而不是顶点缓冲区的长度。

GLES30.glDrawArrays(GLES30.GL_TRIANGLES, 0, vertexCount);

Android 上的 openGl es 在右上角显示一个正方形

openGl es on Android displays a Square at the top right corner

android

opengl-es

gpu