c++ - How do I fit a 2D scene into a QOpenGLWidget window using a shader program?

问题描述

I am trying to fit an entire 2D scene of triangles into a window. I am using a shader program to handle drawing the triangles. I only a fraction of the 900 triangles I expect to see. However, when I use the deprecated OpenGL API to draw squares in a similar scene, it works as expected.

It must have somethig to do with the MVP matrix that I am passing into the vertex shader. See the paintGL() method in the scene.cpp module. That is where I setup the glViewport and the mvpMatrix before drawing the triangles.

I have outlined what I have done below.

Tools

Linux
Qt 5.11.1
OpenGL ES

Setup

The scene is 1M x 1M
900 triangles are added to the scene using a shader program
- It is a grid of 30 x 30 triangles evenly distributed in the scene

Problem

An attempt was made to fit the entire scene inside the window.
The result was that only 75 out of the 900 triangles are visible in the window.

Here is a screenshot of the triangles demo.

Triangles demo source:

The scene.cpp module contains the paintGL method.
The triangles.cpp module is where the shader program is setup and the triangles are constructed.
The full source to the triangles demo is on github.

What worked

I found that using the deprecated OpenGL API, drawing squares using GL_QUADS, does what I am looking for. However, I would like to be using shaders.

Here is a screenshot of the squares demo. It is a grid of 10 x 10 squares in a 1M x 1M scene.

Squares demo source:

The full source to the squares demo is on github.

标签： c++openglglslqt5shader

我发现了这个错误。我在triangles.cpp中分配 VBO。我使用了错误的字节数。

改变：

_vertexBuffer.allocate(_vertexes, _vertexCount);

至：

_vertexBuffer.allocate(_vertexes, _vertexCount * sizeof(QVector3D));

解决了这个问题。