Can't render with QOpenGLBuffers

Question

My target is to render a square with QOpenGLBuffers (index and vertex). But after looking all tutors and docs I missed something. Now it renders nothing.

Here is init() of this buffers:

initializeOpenGLFunctions();

glEnable(GL_DEPTH_TEST);
glEnable(GL_TEXTURE_2D);

m_vao.create();
m_vao.bind();

size_t size = 12; // test value. 5 points * 3 coordinates
m_primitives = new GLfloat[size];

m_primitives[0]  = 0.0f;
m_primitives[1]  = 0.0f;
m_primitives[2]  = 0.0f;
m_primitives[3]  = 0.5f;
m_primitives[4]  = 0.5f;
m_primitives[5]  = 0.0f;
m_primitives[6]  = 0.0f;
m_primitives[7]  = 0.5f;
m_primitives[8]  = 0.0f;
m_primitives[9]  = 0.5f;
m_primitives[10] = 0.0f;
m_primitives[11] = 0.0f;

m_indices = new GLint[6];
m_indices[0] = 0;
m_indices[1] = 1;
m_indices[2] = 2;
m_indices[3] = 0;
m_indices[4] = 3;
m_indices[5] = 1;

m_vertexBuffer = new QOpenGLBuffer(QOpenGLBuffer::VertexBuffer);
m_vertexBuffer->create();
m_vertexBuffer->bind();
m_vertexBuffer->allocate(m_primitives, 12 * sizeof(GLfloat));
m_vertexBuffer->setUsagePattern(QOpenGLBuffer::StreamDraw);

m_indexBuffer = new QOpenGLBuffer(QOpenGLBuffer::IndexBuffer);
m_indexBuffer->create();
m_indexBuffer->bind();
m_indexBuffer->setUsagePattern(QOpenGLBuffer::StaticDraw);
m_indexBuffer->allocate(m_indices, 6 * sizeof(GLint));

m_program = new QOpenGLShaderProgram();
m_program->addShaderFromSourceFile(QOpenGLShader::Vertex, ":/shaders/LabelShader.vs");
m_program->addShaderFromSourceFile(QOpenGLShader::Fragment, ":/shaders/LabelShader.fs");

m_program->link();

QImage i = QGLWidget::convertToGLFormat( m_fontTexture );
m_pijeltexture = new QOpenGLTexture(m_fontTexture, QOpenGLTexture::GenerateMipMaps);
m_pijeltexture->setWrapMode(QOpenGLTexture::ClampToEdge);

And here is render() method:

 m_program->bind();
m_vao.bind();
glActiveTexture(GL_TEXTURE0);
m_pijeltexture->bind(0);
m_vertexBuffer->bind();
m_indexBuffer->bind();

int vertexLocation =  m_program->attributeLocation("Vertex");
m_program->enableAttributeArray(vertexLocation);
m_program->setAttributeBuffer(vertexLocation, GL_FLOAT, 0, 3);

glDrawElements(GL_TRIANGLES, 6, GL_INT, 0);

m_vao.release();
m_vertexBuffer->release();
m_indexBuffer->release();
m_program->disableAttributeArray(0);
m_program->release();

Mybe somebody faced such problem?

What's the contents of your shaders? Also did you try checking `glGetError()`? — vallentin, Apr 13 '17 at 11:16
VS: attribute mediump vec3 Vertex; void main() { gl_Position = vec4(Vertex, 1.0); } — DSUkraine, Apr 13 '17 at 12:16
FS: #version 150 void main(void){ gl_FragColor = vec4(1.0, 0.0, 0.0, 1.0); } — DSUkraine, Apr 13 '17 at 12:16

score 0 · Answer 1 · answered Apr 13 '17 at 12:26

Thanks for help. After using glGetError I found that I was used wrong enum. I missed that indexes could be only 3 types: GL_UNSIGNED_BYTE, GL_UNSIGNED_SHORT, or GL_UNSIGNED_INT.

So problem was in this line: glDrawElements(GL_TRIANGLES, 6, GL_INT, 0);

I changed to: glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, 0);
And now everything fine.

Can't render with QOpenGLBuffers

1 Answers1