android - glDrawElements 不绘制任何东西

Question

我正在使用 c/c++ (NDK) for android 在 opengl es 2.0 中编程。我正在使用 GLM 库!

到目前为止，我可以使用 glDrawArrays 在黑色背景上绘制一个白色三角形，但是当我尝试使用 glDrawElements 绘制相同的三角形时，它不会绘制任何东西。

相关代码:

float triangleCoords[] = {   // in counterclockwise order:
           0,  5, 5, // top
          -5, 0, 5, // bottom left
           5, 0, 5  // bottom right
  };

 float color[] = { 1,1,1, 1.0f };
 GLuint drawOrder[]={0,1,2};

glClear(GL_COLOR_BUFFER_BIT);

glUseProgram(program);

int positionHandle=glGetAttribLocation(program,"vPosition");

int matrixHandle = glGetUniformLocation(program, "uMVPMatrix");

glEnableVertexAttribArray(positionHandle);

glUniformMatrix4fv(matrixHandle,1,GL_FALSE,glm::value_ptr(mvpMatrix));

glVertexAttribPointer(positionHandle,3,GL_FLOAT,GL_FALSE,0,triangleCoords);

int colorHandle =glGetUniformLocation(program, "vColor");

glUniform4fv(colorHandle, 1, color);

//glDrawArrays(GL_TRIANGLES, 0, 3); <== This works

glDrawElements(GL_TRIANGLES,3,GL_UNSIGNED_INT,drawOrder); <== This does not works

glDisableVertexAttribArray(positionHandle);

 //swapbuffers and stuff

着色器非常基础

std::string vertexShaderCode =
        "attribute vec4 vPosition; "
        "uniform mat4 uMVPMatrix;  "
        "void main() {"
        "  gl_Position = uMVPMatrix*vPosition;"
        "}";

    std::string fragmentShaderCode =
        "precision mediump float;"
        "uniform vec4 vColor;"
        "void main() {"
        "  gl_FragColor = vColor;"
        "}";

Answer 1

OpenGLES 不保证索引支持 GL_UNSIGNED_INT。使用 GL_UNSIGNED_SHORT:

GLushort drawOrder[]={0,1,2};

...

glDrawElements(GL_TRIANGLES,3,GL_UNSIGNED_SHORT,drawOrder);