Using openGL to do some image processing, the first experiment is
convert the color image to gray, everything are fine, but I don’t want
to show the widget.
If I don’t call “show()” the QGLWidget would not begin to render the texture
Could I render the texture without showing the widget?
Is QGLWidget a right tool to do that?
part of the codes
#include <QDebug>
#include "toGray.hpp"
toGray::toGray(std::string const &vertex_file, std::string const &fragment_file, QWidget *parent)
:basicGLWidget(vertex_file, fragment_file, parent) //read shaders, compile them, allocate VBO
{
}
void toGray::initializeVertexBuffer()
{
std::vector<GLfloat> const vertex{
-1.0f, 1.0f, 0.0f, 1.0f,
1.0f, 1.0f, 0.0f, 1.0f,
-1.0f, -1.0f, 0.0f, 1.0f,
1.0f, 1.0f, 0.0f, 1.0f,
1.0f, -1.0f, 0.0f, 1.0f,
-1.0f, -1.0f, 0.0f, 1.0f,
};
initializeVertexBufferImpl(vertex); //copy the data into QOpenGLBuffer
QImage img(":/simpleGPGPU/images/emili.jpg");
texture_addr_ = bindTexture(img);
resize(img.width(), img.height());
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
}
void toGray::paintGL()
{
qglClearColor(Qt::white);
glClear(GL_COLOR_BUFFER_BIT);
program_.bind();
bind_buffer();
program_.enableAttributeArray("qt_Vertex");
program_.setAttributeBuffer( "qt_Vertex", GL_FLOAT, 0, 4);
glActiveTexture(GL_TEXTURE0);
glBindTexture(GL_TEXTURE_2D, texture_addr_);
glDrawArrays(GL_TRIANGLES, 0, get_buffer(0).size());
program_.disableAttributeArray("qt_Vertex");
program_.release();
glActiveTexture(0);
release_buffer();
}
vertex shader
attribute highp vec4 qt_Vertex;
varying highp vec2 qt_TexCoord0;
void main(void)
{
gl_Position = qt_Vertex;
qt_TexCoord0 = (qt_Vertex.xy + vec2(1.0)) * 0.5;
}
fragment shader
uniform sampler2D source;
varying highp vec2 qt_TexCoord0;
vec3 toGray(vec3 rgb)
{
return vec3(rgb.r * 0.299 + rgb.g * 0.587 + rgb.b * 0.114);
}
void main(void)
{
vec3 gray = toGray(texture2D(source, qt_TexCoord0).rgb);
gl_FragColor = vec4(gray, 0.0);
}
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