• Advertisement
Sign in to follow this  

OpenGL SOLVED: Render a vector to screen in opengl

This topic is 1302 days old which is more than the 365 day threshold we allow for new replies. Please post a new topic.

If you intended to correct an error in the post then please contact us.

Recommended Posts

Hello,

I have this simple code (just a green cube in scene):

// Include standard headers
#include <stdio.h>
#include <stdlib.h>
#include <iostream>
#include <vector>
#include <windows.h>
// Include GLEW
#include <glew.h>
 
// Include GLFW
#include <glfw3.h>
GLFWwindow* window;
 
// Include GLM
#include <glm.hpp>
#include <gtc/matrix_transform.hpp>
using namespace glm;
 
#include "shader.hpp"
 
int main( void )
{
	// Initialise GLFW
	if( !glfwInit() )
	{
		fprintf( stderr, "Failed to initialize GLFW\n" );
		return -1;
	}
 
	glfwWindowHint(GLFW_SAMPLES, 4);
	glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
	glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
	glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);
 
	// Open a window and create its OpenGL context
	window = glfwCreateWindow( 1024, 768, "Cube", NULL, NULL);
	if( window == NULL ){
		fprintf( stderr, "Failed to open GLFW window. If you have an Intel GPU, they are not 3.3 compatible. Try the 2.1 version of the tutorials.\n" );
		glfwTerminate();
		return -1;
	}
	glfwMakeContextCurrent(window);
 
	// Initialize GLEW
	glewExperimental = true; // Needed for core profile
	if (glewInit() != GLEW_OK) {
		fprintf(stderr, "Failed to initialize GLEW\n");
		return -1;
	}
 
	// Ensure we can capture the escape key being pressed below
	glfwSetInputMode(window, GLFW_STICKY_KEYS, GL_TRUE);
 
	// Dark blue background
	glClearColor(0.0f, 0.0f, 0.4f, 0.0f);
 
	// Enable depth test
	glEnable(GL_DEPTH_TEST);
	// Accept fragment if it closer to the camera than the former one
	glDepthFunc(GL_LESS); 
 
	GLuint VertexArrayID;
	glGenVertexArrays(1, &VertexArrayID);
	glBindVertexArray(VertexArrayID);
 
	// Create and compile our GLSL program from the shaders
	GLuint programID = LoadShaders( "TransformVertexShader.vertexshader", "ColorFragmentShader.fragmentshader" );
 
	// Get a handle for our "MVP" uniform
	GLuint MatrixID = glGetUniformLocation(programID, "MVP");
 
	// Projection matrix : 45° Field of View, 4:3 ratio, display range : 0.1 unit <-> 100 units
	glm::mat4 Projection = glm::perspective(45.0f, 4.0f / 3.0f, 0.1f, 100.0f);
	// Camera matrix
	glm::mat4 View       = glm::lookAt(
								glm::vec3(4,3,-3), // Camera is at (4,3,-3), in World Space
								glm::vec3(0,0,0), // and looks at the origin
								glm::vec3(0,1,0)  // Head is up (set to 0,-1,0 to look upside-down)
						   );
	// Model matrix : an identity matrix (model will be at the origin)
	glm::mat4 Model      = glm::mat4(1.0f);
	// Our ModelViewProjection : multiplication of our 3 matrices
	glm::mat4 MVP        = Projection * View * Model; // Remember, matrix multiplication is the other way around
 
	// Our vertices. Tree consecutive floats give a 3D vertex; Three consecutive vertices give a triangle.
	// A cube has 6 faces with 2 triangles each, so this makes 6*2=12 triangles, and 12*3 vertices
	static const GLfloat g_vertex_buffer_data[] = { 
		-1.0f,-1.0f,-1.0f,
		-1.0f,-1.0f, 1.0f,
		-1.0f, 1.0f, 1.0f,
		 1.0f, 1.0f,-1.0f,
		-1.0f,-1.0f,-1.0f,
		-1.0f, 1.0f,-1.0f,
		 1.0f,-1.0f, 1.0f,
		-1.0f,-1.0f,-1.0f,
		 1.0f,-1.0f,-1.0f,
		 1.0f, 1.0f,-1.0f,
		 1.0f,-1.0f,-1.0f,
		-1.0f,-1.0f,-1.0f,
		-1.0f,-1.0f,-1.0f,
		-1.0f, 1.0f, 1.0f,
		-1.0f, 1.0f,-1.0f,
		 1.0f,-1.0f, 1.0f,
		-1.0f,-1.0f, 1.0f,
		-1.0f,-1.0f,-1.0f,
		-1.0f, 1.0f, 1.0f,
		-1.0f,-1.0f, 1.0f,
		 1.0f,-1.0f, 1.0f,
		 1.0f, 1.0f, 1.0f,
		 1.0f,-1.0f,-1.0f,
		 1.0f, 1.0f,-1.0f,
		 1.0f,-1.0f,-1.0f,
		 1.0f, 1.0f, 1.0f,
		 1.0f,-1.0f, 1.0f,
		 1.0f, 1.0f, 1.0f,
		 1.0f, 1.0f,-1.0f,
		-1.0f, 1.0f,-1.0f,
		 1.0f, 1.0f, 1.0f,
		-1.0f, 1.0f,-1.0f,
		-1.0f, 1.0f, 1.0f,
		 1.0f, 1.0f, 1.0f,
		-1.0f, 1.0f, 1.0f,
		 1.0f,-1.0f, 1.0f
	};
 
	// One color for each vertex. They were generated randomly.
	static const GLfloat g_color_buffer_data[] = { 
		0.583f,  0.771f,  0.014f,
				0.583f,  0.771f,  0.014f,
				0.583f,  0.771f,  0.014f,
				0.583f,  0.771f,  0.014f,
				0.583f,  0.771f,  0.014f,
				0.583f,  0.771f,  0.014f,
				0.583f,  0.771f,  0.014f,
				0.583f,  0.771f,  0.014f,
				0.583f,  0.771f,  0.014f,
				0.583f,  0.771f,  0.014f,
				0.583f,  0.771f,  0.014f,
				0.583f,  0.771f,  0.014f,
				0.583f,  0.771f,  0.014f,
				0.583f,  0.771f,  0.014f,
				0.583f,  0.771f,  0.014f,
				0.583f,  0.771f,  0.014f,
				0.583f,  0.771f,  0.014f,
				0.583f,  0.771f,  0.014f,
				0.583f,  0.771f,  0.014f,
				0.583f,  0.771f,  0.014f,
				0.583f,  0.771f,  0.014f,
				0.583f,  0.771f,  0.014f,
				0.583f,  0.771f,  0.014f,
				0.583f,  0.771f,  0.014f,
				0.583f,  0.771f,  0.014f,
				0.583f,  0.771f,  0.014f,
				0.583f,  0.771f,  0.014f,
				0.583f,  0.771f,  0.014f,
				0.583f,  0.771f,  0.014f,
				0.583f,  0.771f,  0.014f,
				0.583f,  0.771f,  0.014f,
				0.583f,  0.771f,  0.014f,
				0.583f,  0.771f,  0.014f,
				0.583f,  0.771f,  0.014f,
				0.583f,  0.771f,  0.014f,
				0.583f,  0.771f,  0.014f
	};
 
	GLuint vertexbuffer;
	glGenBuffers(1, &vertexbuffer);
	glBindBuffer(GL_ARRAY_BUFFER, vertexbuffer);
	glBufferData(GL_ARRAY_BUFFER, sizeof(g_vertex_buffer_data), g_vertex_buffer_data, GL_STATIC_DRAW);
 
	GLuint colorbuffer;
	glGenBuffers(1, &colorbuffer);
	glBindBuffer(GL_ARRAY_BUFFER, colorbuffer);
	glBufferData(GL_ARRAY_BUFFER, sizeof(g_color_buffer_data), g_color_buffer_data, GL_STATIC_DRAW);
 
	do{
              std::vector<GLfloat> pixel(1024*768*3);
              glReadPixels(0, 0, 1024, 768, GL_RGB, GL_FLOAT, &pixel[0]);
              std::cout << "R G B: " << pixel[0]<< " "<<pixel[1]<< " "<<pixel[2] << "\n"; //not really needed
       
		// Clear the screen
		glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
 
		// Use our shader
		glUseProgram(programID);
 
		// Send our transformation to the currently bound shader, 
		// in the "MVP" uniform
		glUniformMatrix4fv(MatrixID, 1, GL_FALSE, &MVP[0][0]);
 
		// 1rst attribute buffer : vertices
		glEnableVertexAttribArray(0);
		glBindBuffer(GL_ARRAY_BUFFER, vertexbuffer);
		glVertexAttribPointer(
			0,                  // attribute. No particular reason for 0, but must match the layout in the shader.
			3,                  // size
			GL_FLOAT,           // type
			GL_FALSE,           // normalized?
			0,                  // stride
			(void*)0            // array buffer offset
		);
 
		// 2nd attribute buffer : colors
		glEnableVertexAttribArray(1);
		glBindBuffer(GL_ARRAY_BUFFER, colorbuffer);
		glVertexAttribPointer(
			1,                                // attribute. No particular reason for 1, but must match the layout in the shader.
			3,                                // size
			GL_FLOAT,                         // type
			GL_FALSE,                         // normalized?
			0,                                // stride
			(void*)0                          // array buffer offset
		);
 
		// Draw the triangle !
		glDrawArrays(GL_TRIANGLES, 0, 12*3); // 12*3 indices starting at 0 -> 12 triangles
 
		glDisableVertexAttribArray(0);
		glDisableVertexAttribArray(1);
 
		// Swap buffers
		glfwSwapBuffers(window);
		glfwPollEvents();
 
	} // Check if the ESC key was pressed or the window was closed
	while( glfwGetKey(window, GLFW_KEY_ESCAPE ) != GLFW_PRESS &&
		   glfwWindowShouldClose(window) == 0 );
 
	// Cleanup VBO and shader
	glDeleteBuffers(1, &vertexbuffer);
	glDeleteBuffers(1, &colorbuffer);
	glDeleteProgram(programID);
	glDeleteVertexArrays(1, &VertexArrayID);
 
	// Close OpenGL window and terminate GLFW
	glfwTerminate();
 
	return 0;
}

As you can see I have this lines:

std::vector<GLfloat> pixel(1024*768*3);
glReadPixels(0, 0, 1024, 200, GL_RGB, GL_FLOAT, &pixel[0]);

Now, how Can I pass the pixel vector to Opengl for render him and not the standard way?

I need this because I want to manipulate in same way the pixel vector and than pass him to opengl for render.

But I don't know how to do that.

 

Thanks

Edited by Alfox

Share this post


Link to post
Share on other sites
Advertisement

You know that glReadPixels just reads what's on the screen already, so what are you actually trying to do? Copy the screen for re-rendering at a later time?

 

What are you considering "the standard way"?

 

Modern, you would populate the texture with the pixel data, and render the texture with a shader.. But then again you also wouldn't be using glReadPixels.

 

So - maybe glDrawPixels?

Share this post


Link to post
Share on other sites

Hi thanks for reply,

I used glReadPixels because searching on google this function was the result. But if there is another way I can delete this function

 

 

you would populate the texture with the pixel data, and render the texture with a shader

 

yes, I want populate the texture with the pixel data, precisely I want

1. collect the pixels color information in a structure (like glReadPixels does)

2. modify same pixels color (for instance in my previous example, modify the green pixels to become blue)

3. render the pixels data modified.

 

 

What are you considering "the standard way"?

 

render to screen with the vertex buffer and color buffer.

 

I tried also to follow a tutorial on how render to texture, but also in this way I don't know how to modify the code for manipulate the pixels before render them on screen.

Share this post


Link to post
Share on other sites

There is glDrawPixels

 

Keep in mind this function is deprecated and I wouldn't do any image processing using glReadPixels with glDrawPixels in any production code.

 

 

You should use a shader program to process the render output. To do that, you render your scene to an offscreen framebuffer bound to a texture. You then use that texture as the input to drawing a quad over the entire screen.

 

Here is an example of how to do this.

Render to Texture

Share this post


Link to post
Share on other sites

Hello

yes I read about glDrawPixels and I don't want to use it, because as you said is deprecated.

 

I already read that tutorial, and tried, but how can I access to pixels after saved in framebuffer but before rendered on the quad?

for instance:

- save all in the framebuffer

- access to saved pixels and modify samething

- render the modified framebuffer to the quad

Share this post


Link to post
Share on other sites

If you are creating a framebuffer object you will most likly attach a texture (previously generated with glGenTextures ()...) as color rendertarget using the glFramebufferTexture() function.

 

I dont know if I understood you right but I guess you want to do something like this:

1 Bind the fbo for offscreen rendering

2 Render anything you like

3 Unbind the fbo

4 Retrieve texture data from your rendered image into main memory (you can do that using glGetTexImage() with the texture you have attached as colortarget to your fbo)

5 Modify the texture data in main memory and update the texture on you graphics card (with glTexSubImage2D ())

6 Render the modified texture in a fullscreen quad to your window backbuffer

 

 

This will work, although I highly recommend not to do this, and do what ever you want to modify in your texture on the gpu.

If it is just a pixel operation you want to do, then you can do the same as I described above but omit the steps 4 and 5 and do all modifications in the fragment shader stage.

 

Share this post


Link to post
Share on other sites

Hello!

yes this is what I want to do

I created this (whit the help of the tutorial linked above by HappyCoder )

// Include standard headers
#include <stdio.h>
#include <stdlib.h>
#include <iostream>
#include <vector>
#include <windows.h>
// Include GLEW
#include <glew.h>

// Include GLFW
#include <glfw3.h>
GLFWwindow* window;

// Include GLM
#include <glm.hpp>
#include <gtc/matrix_transform.hpp>
using namespace glm;

#include "shader.hpp"

int main( void )
{
	// Initialise GLFW
	if( !glfwInit() )
	{
		fprintf( stderr, "Failed to initialize GLFW\n" );
		return -1;
	}

	glfwWindowHint(GLFW_SAMPLES, 4);
	glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
	glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
	glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);

	// Open a window and create its OpenGL context
	window = glfwCreateWindow( 1024, 768, "Cube", NULL, NULL);
	if( window == NULL ){
		fprintf( stderr, "Failed to open GLFW window. If you have an Intel GPU, they are not 3.3 compatible. Try the 2.1 version of the tutorials.\n" );
		glfwTerminate();
		return -1;
	}
	glfwMakeContextCurrent(window);

	// Initialize GLEW
	glewExperimental = true; // Needed for core profile
	if (glewInit() != GLEW_OK) {
		fprintf(stderr, "Failed to initialize GLEW\n");
		return -1;
	}

	// Ensure we can capture the escape key being pressed below
	glfwSetInputMode(window, GLFW_STICKY_KEYS, GL_TRUE);

	// Dark blue background
	glClearColor(0.0f, 0.0f, 0.4f, 0.0f);

	// Enable depth test
	glEnable(GL_DEPTH_TEST);
	// Accept fragment if it closer to the camera than the former one
	//glDepthFunc(GL_LESS); 

	GLuint VertexArrayID;
	glGenVertexArrays(1, &VertexArrayID);
	glBindVertexArray(VertexArrayID);

	// Create and compile our GLSL program from the shaders
	GLuint programID = LoadShaders( "TransformVertexShader.vertexshader", "ColorFragmentShader.fragmentshader" );

	// Get a handle for our "MVP" uniform
	GLuint MatrixID = glGetUniformLocation(programID, "MVP");

	// Projection matrix : 45° Field of View, 4:3 ratio, display range : 0.1 unit <-> 100 units
	glm::mat4 Projection = glm::perspective(45.0f, 4.0f / 3.0f, 0.1f, 100.0f);
	// Camera matrix
	glm::mat4 View       = glm::lookAt(
								glm::vec3(4,3,-3), // Camera is at (4,3,-3), in World Space
								glm::vec3(0,0,0), // and looks at the origin
								glm::vec3(0,1,0)  // Head is up (set to 0,-1,0 to look upside-down)
						   );
	// Model matrix : an identity matrix (model will be at the origin)
	glm::mat4 Model      = glm::mat4(1.0f);
	// Our ModelViewProjection : multiplication of our 3 matrices
	glm::mat4 MVP        = Projection * View * Model; // Remember, matrix multiplication is the other way around

	// Our vertices. Tree consecutive floats give a 3D vertex; Three consecutive vertices give a triangle.
	// A cube has 6 faces with 2 triangles each, so this makes 6*2=12 triangles, and 12*3 vertices
	static const GLfloat g_vertex_buffer_data[] = { 
		-1.0f,-1.0f,-1.0f,
		-1.0f,-1.0f, 1.0f,
		-1.0f, 1.0f, 1.0f,
		 1.0f, 1.0f,-1.0f,
		-1.0f,-1.0f,-1.0f,
		-1.0f, 1.0f,-1.0f,
		 1.0f,-1.0f, 1.0f,
		-1.0f,-1.0f,-1.0f,
		 1.0f,-1.0f,-1.0f,
		 1.0f, 1.0f,-1.0f,
		 1.0f,-1.0f,-1.0f,
		-1.0f,-1.0f,-1.0f,
		-1.0f,-1.0f,-1.0f,
		-1.0f, 1.0f, 1.0f,
		-1.0f, 1.0f,-1.0f,
		 1.0f,-1.0f, 1.0f,
		-1.0f,-1.0f, 1.0f,
		-1.0f,-1.0f,-1.0f,
		-1.0f, 1.0f, 1.0f,
		-1.0f,-1.0f, 1.0f,
		 1.0f,-1.0f, 1.0f,
		 1.0f, 1.0f, 1.0f,
		 1.0f,-1.0f,-1.0f,
		 1.0f, 1.0f,-1.0f,
		 1.0f,-1.0f,-1.0f,
		 1.0f, 1.0f, 1.0f,
		 1.0f,-1.0f, 1.0f,
		 1.0f, 1.0f, 1.0f,
		 1.0f, 1.0f,-1.0f,
		-1.0f, 1.0f,-1.0f,
		 1.0f, 1.0f, 1.0f,
		-1.0f, 1.0f,-1.0f,
		-1.0f, 1.0f, 1.0f,
		 1.0f, 1.0f, 1.0f,
		-1.0f, 1.0f, 1.0f,
		 1.0f,-1.0f, 1.0f
	};

	// One color for each vertex. They were generated randomly.
	static const GLfloat g_color_buffer_data[] = { 
		0.583f,  0.771f,  0.014f,
				0.583f,  0.771f,  0.014f,
				0.583f,  0.771f,  0.014f,
				0.583f,  0.771f,  0.014f,
				0.583f,  0.771f,  0.014f,
				0.583f,  0.771f,  0.014f,
				0.583f,  0.771f,  0.014f,
				0.583f,  0.771f,  0.014f,
				0.583f,  0.771f,  0.014f,
				0.583f,  0.771f,  0.014f,
				0.583f,  0.771f,  0.014f,
				0.583f,  0.771f,  0.014f,
				0.583f,  0.771f,  0.014f,
				0.583f,  0.771f,  0.014f,
				0.583f,  0.771f,  0.014f,
				0.583f,  0.771f,  0.014f,
				0.583f,  0.771f,  0.014f,
				0.583f,  0.771f,  0.014f,
				0.583f,  0.771f,  0.014f,
				0.583f,  0.771f,  0.014f,
				0.583f,  0.771f,  0.014f,
				0.583f,  0.771f,  0.014f,
				0.583f,  0.771f,  0.014f,
				0.583f,  0.771f,  0.014f,
				0.583f,  0.771f,  0.014f,
				0.583f,  0.771f,  0.014f,
				0.583f,  0.771f,  0.014f,
				0.583f,  0.771f,  0.014f,
				0.583f,  0.771f,  0.014f,
				0.583f,  0.771f,  0.014f,
				0.583f,  0.771f,  0.014f,
				0.583f,  0.771f,  0.014f,
				0.583f,  0.771f,  0.014f,
				0.583f,  0.771f,  0.014f,
				0.583f,  0.771f,  0.014f,
				0.583f,  0.771f,  0.014f
	};

	GLuint vertexbuffer;
	glGenBuffers(1, &vertexbuffer);
	glBindBuffer(GL_ARRAY_BUFFER, vertexbuffer);
	glBufferData(GL_ARRAY_BUFFER, sizeof(g_vertex_buffer_data), g_vertex_buffer_data, GL_STATIC_DRAW);

	GLuint colorbuffer;
	glGenBuffers(1, &colorbuffer);
	glBindBuffer(GL_ARRAY_BUFFER, colorbuffer);
	glBufferData(GL_ARRAY_BUFFER, sizeof(g_color_buffer_data), g_color_buffer_data, GL_STATIC_DRAW);

	glUseProgram(programID);


		// ---------------------------------------------
	// Render to Texture - specific code begins here
	// ---------------------------------------------

	// The framebuffer, which regroups 0, 1, or more textures, and 0 or 1 depth buffer.
	GLuint FramebufferName = 0;
	glGenFramebuffers(1, &FramebufferName);
	glBindFramebuffer(GL_FRAMEBUFFER, FramebufferName);

	// The texture we're going to render to
	GLuint renderedTexture;
	glGenTextures(1, &renderedTexture);
	
	// "Bind" the newly created texture : all future texture functions will modify this texture
	glBindTexture(GL_TEXTURE_2D, renderedTexture);

	// Give an empty image to OpenGL ( the last "0" means "empty" )
	glTexImage2D(GL_TEXTURE_2D, 0,GL_RGB, 1024, 768, 0,GL_RGBA, GL_UNSIGNED_BYTE, 0);

	// Poor filtering
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST); 
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);

	// The depth buffer
	GLuint depthrenderbuffer;
	glGenRenderbuffers(1, &depthrenderbuffer);
	glBindRenderbuffer(GL_RENDERBUFFER, depthrenderbuffer);
	glRenderbufferStorage(GL_RENDERBUFFER, GL_DEPTH_COMPONENT, 1024, 768);
	glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT, GL_RENDERBUFFER, depthrenderbuffer);

	//----------------------------

	// Set "renderedTexture" as our colour attachement #0
	glFramebufferTexture(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, renderedTexture, 0);

	// Set the list of draw buffers.
	GLenum DrawBuffers[1] = {GL_COLOR_ATTACHMENT0};
	glDrawBuffers(1, DrawBuffers); // "1" is the size of DrawBuffers

	// Always check that our framebuffer is ok
	if(glCheckFramebufferStatus(GL_FRAMEBUFFER) != GL_FRAMEBUFFER_COMPLETE)
	{
		printf("\nFrameBuffer Error\n");
		return false;
	}

	
	// The fullscreen quad's FBO
	static const GLfloat g_quad_vertex_buffer_data[] = { 
		-1.0f, -1.0f, 0.0f,
		 1.0f, -1.0f, 0.0f,
		-1.0f,  1.0f, 0.0f,
		-1.0f,  1.0f, 0.0f,
		 1.0f, -1.0f, 0.0f,
		 1.0f,  1.0f, 0.0f,
	};

	GLuint quad_vertexbuffer;
	glGenBuffers(1, &quad_vertexbuffer);
	glBindBuffer(GL_ARRAY_BUFFER, quad_vertexbuffer);
	glBufferData(GL_ARRAY_BUFFER, sizeof(g_quad_vertex_buffer_data), g_quad_vertex_buffer_data, GL_STATIC_DRAW);

	// Create and compile our GLSL program from the shaders
	GLuint quad_programID = LoadShaders( "Passthrough.vertexshader", "WobblyTexture.fragmentshader" );
	GLuint texID = glGetUniformLocation(quad_programID, "renderedTexture");


	do{

		//std::vector<GLfloat> pixel(1024*768*3); 
		//glReadPixels(0, 0, 1024, 768, GL_RGB, GL_FLOAT, &pixel[0]);
	

		// Render to our framebuffer
		glBindFramebuffer(GL_FRAMEBUFFER, FramebufferName);
		glViewport(0,0,1024,768); // Render on the whole framebuffer, complete from the lower left corner to the upper right

		// Clear the screen
		glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

		// Use our shader
		glUseProgram(programID);

		// Send our transformation to the currently bound shader, 
		// in the "MVP" uniform
		glUniformMatrix4fv(MatrixID, 1, GL_FALSE, &MVP[0][0]);

		// 1rst attribute buffer : vertices
		glEnableVertexAttribArray(0);
		glBindBuffer(GL_ARRAY_BUFFER, vertexbuffer);
		glVertexAttribPointer(
			0,                  // attribute. No particular reason for 0, but must match the layout in the shader.
			3,                  // size
			GL_FLOAT,           // type
			GL_FALSE,           // normalized?
			0,                  // stride
			(void*)0            // array buffer offset
		);

		// 2nd attribute buffer : colors
		glEnableVertexAttribArray(1);
		glBindBuffer(GL_ARRAY_BUFFER, colorbuffer);
		glVertexAttribPointer(
			1,                                // attribute. No particular reason for 1, but must match the layout in the shader.
			3,                                // size
			GL_FLOAT,                         // type
			GL_FALSE,                         // normalized?
			0,                                // stride
			(void*)0                          // array buffer offset
		);

		// Draw the triangle !
		glDrawArrays(GL_TRIANGLES, 0, 12*3); // 12*3 indices starting at 0 -> 12 triangles

		glDisableVertexAttribArray(0);
		glDisableVertexAttribArray(1);

		

		// Render to the screen
		glBindFramebuffer(GL_FRAMEBUFFER, 0);
		glViewport(0,0,1024,768); // Render on the whole framebuffer, complete from the lower left corner to the upper right

		// Clear the screen
		glClear( GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

		// Use our shader
		glUseProgram(quad_programID);

		
		// Bind our texture in Texture Unit 0
		glActiveTexture(GL_TEXTURE0);
		glBindTexture(GL_TEXTURE_2D, renderedTexture);
		// Set our "renderedTexture" sampler to user Texture Unit 0
		glUniform1i(texID, 0);

		// 1rst attribute buffer : vertices
		glEnableVertexAttribArray(0);
		glBindBuffer(GL_ARRAY_BUFFER, quad_vertexbuffer);
		glVertexAttribPointer(
			0,                  // attribute 0. No particular reason for 0, but must match the layout in the shader.
			3,                  // size
			GL_FLOAT,           // type
			GL_FALSE,           // normalized?
			0,                  // stride
			(void*)0            // array buffer offset
		);

		
		// Draw the triangles !
		glDrawArrays(GL_TRIANGLES, 0, 6); // 2*3 indices starting at 0 -> 2 triangles

		glDisableVertexAttribArray(0);

		

		// Swap buffers
		glfwSwapBuffers(window);
		glfwPollEvents();

	} // Check if the ESC key was pressed or the window was closed
	while( glfwGetKey(window, GLFW_KEY_ESCAPE ) != GLFW_PRESS &&
		   glfwWindowShouldClose(window) == 0 );

		// Cleanup VBO and shader
	glDeleteBuffers(1, &vertexbuffer);
	glDeleteBuffers(1, &colorbuffer);
	glDeleteProgram(programID);


	glDeleteFramebuffers(1, &FramebufferName);
	glDeleteTextures(1, &renderedTexture);
	glDeleteRenderbuffers(1, &depthrenderbuffer);
	glDeleteBuffers(1, &quad_vertexbuffer);
	glDeleteVertexArrays(1, &VertexArrayID);

	// Close OpenGL window and terminate GLFW
	glfwTerminate();

	return 0;
}


So now I render the cube in the framebuffer than, render the framebuffer on the quad.

 

As you suggest I have to retrieve data after call this:

		// Draw the triangle !
		glDrawArrays(GL_TRIANGLES, 0, 12*3); // 12*3 indices starting at 0 -> 12 triangles

		glDisableVertexAttribArray(0);
		glDisableVertexAttribArray(1);

with glGetTexImage()

modify the texture, than update the modified texture with glTexSubImage2D ()

 

and than continue with:

		// Render to the screen
		glBindFramebuffer(GL_FRAMEBUFFER, 0);
		glViewport(0,0,1024,768); // Render on the whole framebuffer, complete from the lower left corner to the upper right

		// Clear the screen
		glClear( GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

		// Use our shader
		glUseProgram(quad_programID);

		
		// Bind our texture in Texture Unit 0
		glActiveTexture(GL_TEXTURE0);
		glBindTexture(GL_TEXTURE_2D, renderedTexture);
		// Set our "renderedTexture" sampler to user Texture Unit 0
		glUniform1i(texID, 0);

		// 1rst attribute buffer : vertices
		glEnableVertexAttribArray(0);
		glBindBuffer(GL_ARRAY_BUFFER, quad_vertexbuffer);
		glVertexAttribPointer(
			0,                  // attribute 0. No particular reason for 0, but must match the layout in the shader.
			3,                  // size
			GL_FLOAT,           // type
			GL_FALSE,           // normalized?
			0,                  // stride
			(void*)0            // array buffer offset
		);

		
		// Draw the triangles !
		glDrawArrays(GL_TRIANGLES, 0, 6); // 2*3 indices starting at 0 -> 2 triangles

		glDisableVertexAttribArray(0);

		

		// Swap buffers
		glfwSwapBuffers(window);
		glfwPollEvents();

is this right?

Share this post


Link to post
Share on other sites

Yes, but make sure you call glBindFrameBuffer(GL_FRAMEBUFFER, 0) befor glGetTexImage (), or else it will fail. Mapping/binding textures that are attached to a bound fbo will fail.

Share this post


Link to post
Share on other sites

Hi!

This works!! thanks a lot!

this is the update of the previous code:

		glDisableVertexAttribArray(0);
		glDisableVertexAttribArray(1);

		// Render to the screen
		glBindFramebuffer(GL_FRAMEBUFFER, 0);
		glViewport(0,0,1024,768); // Render on the whole framebuffer, complete from the lower left corner to the upper right
		/*---------------------------------------------------------*/
		int size = 1024*768*3;
		std::vector<GLfloat> pix(size);
		glGetTexImage (GL_TEXTURE_2D, 0, GL_RGB, GL_FLOAT, &pix[0]);
		for(int c = 0; c < size; c++){	
			if (pix[c] > 0.5)
				pix[c] = 1.0; //just a little modify for try, the cube should be yellow now (it was green)
		}
		glTexSubImage2D (GL_TEXTURE_2D,0,0,0,1024,768,GL_RGB,GL_FLOAT,&pix[0]);


		/*---------------------------------------------------------*/	
		// Clear the screen
		glClear( GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

Share this post


Link to post
Share on other sites
Sign in to follow this  

  • Advertisement
  • Advertisement
  • Popular Now

  • Advertisement
  • Similar Content

    • By Balma Alparisi
      i got error 1282 in my code.
      sf::ContextSettings settings; settings.majorVersion = 4; settings.minorVersion = 5; settings.attributeFlags = settings.Core; sf::Window window; window.create(sf::VideoMode(1600, 900), "Texture Unit Rectangle", sf::Style::Close, settings); window.setActive(true); window.setVerticalSyncEnabled(true); glewInit(); GLuint shaderProgram = createShaderProgram("FX/Rectangle.vss", "FX/Rectangle.fss"); float vertex[] = { -0.5f,0.5f,0.0f, 0.0f,0.0f, -0.5f,-0.5f,0.0f, 0.0f,1.0f, 0.5f,0.5f,0.0f, 1.0f,0.0f, 0.5,-0.5f,0.0f, 1.0f,1.0f, }; GLuint indices[] = { 0,1,2, 1,2,3, }; GLuint vao; glGenVertexArrays(1, &vao); glBindVertexArray(vao); GLuint vbo; glGenBuffers(1, &vbo); glBindBuffer(GL_ARRAY_BUFFER, vbo); glBufferData(GL_ARRAY_BUFFER, sizeof(vertex), vertex, GL_STATIC_DRAW); GLuint ebo; glGenBuffers(1, &ebo); glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, ebo); glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(indices), indices,GL_STATIC_DRAW); glVertexAttribPointer(0, 3, GL_FLOAT, false, sizeof(float) * 5, (void*)0); glEnableVertexAttribArray(0); glVertexAttribPointer(1, 2, GL_FLOAT, false, sizeof(float) * 5, (void*)(sizeof(float) * 3)); glEnableVertexAttribArray(1); GLuint texture[2]; glGenTextures(2, texture); glActiveTexture(GL_TEXTURE0); glBindTexture(GL_TEXTURE_2D, texture[0]); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR); sf::Image* imageOne = new sf::Image; bool isImageOneLoaded = imageOne->loadFromFile("Texture/container.jpg"); if (isImageOneLoaded) { glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, imageOne->getSize().x, imageOne->getSize().y, 0, GL_RGBA, GL_UNSIGNED_BYTE, imageOne->getPixelsPtr()); glGenerateMipmap(GL_TEXTURE_2D); } delete imageOne; glActiveTexture(GL_TEXTURE1); glBindTexture(GL_TEXTURE_2D, texture[1]); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR); sf::Image* imageTwo = new sf::Image; bool isImageTwoLoaded = imageTwo->loadFromFile("Texture/awesomeface.png"); if (isImageTwoLoaded) { glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, imageTwo->getSize().x, imageTwo->getSize().y, 0, GL_RGBA, GL_UNSIGNED_BYTE, imageTwo->getPixelsPtr()); glGenerateMipmap(GL_TEXTURE_2D); } delete imageTwo; glUniform1i(glGetUniformLocation(shaderProgram, "inTextureOne"), 0); glUniform1i(glGetUniformLocation(shaderProgram, "inTextureTwo"), 1); GLenum error = glGetError(); std::cout << error << std::endl; sf::Event event; bool isRunning = true; while (isRunning) { while (window.pollEvent(event)) { if (event.type == event.Closed) { isRunning = false; } } glClear(GL_COLOR_BUFFER_BIT); if (isImageOneLoaded && isImageTwoLoaded) { glActiveTexture(GL_TEXTURE0); glBindTexture(GL_TEXTURE_2D, texture[0]); glActiveTexture(GL_TEXTURE1); glBindTexture(GL_TEXTURE_2D, texture[1]); glUseProgram(shaderProgram); } glBindVertexArray(vao); glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, nullptr); glBindVertexArray(0); window.display(); } glDeleteVertexArrays(1, &vao); glDeleteBuffers(1, &vbo); glDeleteBuffers(1, &ebo); glDeleteProgram(shaderProgram); glDeleteTextures(2,texture); return 0; } and this is the vertex shader
      #version 450 core layout(location=0) in vec3 inPos; layout(location=1) in vec2 inTexCoord; out vec2 TexCoord; void main() { gl_Position=vec4(inPos,1.0); TexCoord=inTexCoord; } and the fragment shader
      #version 450 core in vec2 TexCoord; uniform sampler2D inTextureOne; uniform sampler2D inTextureTwo; out vec4 FragmentColor; void main() { FragmentColor=mix(texture(inTextureOne,TexCoord),texture(inTextureTwo,TexCoord),0.2); } I was expecting awesomeface.png on top of container.jpg

    • By khawk
      We've just released all of the source code for the NeHe OpenGL lessons on our Github page at https://github.com/gamedev-net/nehe-opengl. code - 43 total platforms, configurations, and languages are included.
      Now operated by GameDev.net, NeHe is located at http://nehe.gamedev.net where it has been a valuable resource for developers wanting to learn OpenGL and graphics programming.

      View full story
    • By TheChubu
      The Khronos™ Group, an open consortium of leading hardware and software companies, announces from the SIGGRAPH 2017 Conference the immediate public availability of the OpenGL® 4.6 specification. OpenGL 4.6 integrates the functionality of numerous ARB and EXT extensions created by Khronos members AMD, Intel, and NVIDIA into core, including the capability to ingest SPIR-V™ shaders.
      SPIR-V is a Khronos-defined standard intermediate language for parallel compute and graphics, which enables content creators to simplify their shader authoring and management pipelines while providing significant source shading language flexibility. OpenGL 4.6 adds support for ingesting SPIR-V shaders to the core specification, guaranteeing that SPIR-V shaders will be widely supported by OpenGL implementations.
      OpenGL 4.6 adds the functionality of these ARB extensions to OpenGL’s core specification:
      GL_ARB_gl_spirv and GL_ARB_spirv_extensions to standardize SPIR-V support for OpenGL GL_ARB_indirect_parameters and GL_ARB_shader_draw_parameters for reducing the CPU overhead associated with rendering batches of geometry GL_ARB_pipeline_statistics_query and GL_ARB_transform_feedback_overflow_querystandardize OpenGL support for features available in Direct3D GL_ARB_texture_filter_anisotropic (based on GL_EXT_texture_filter_anisotropic) brings previously IP encumbered functionality into OpenGL to improve the visual quality of textured scenes GL_ARB_polygon_offset_clamp (based on GL_EXT_polygon_offset_clamp) suppresses a common visual artifact known as a “light leak” associated with rendering shadows GL_ARB_shader_atomic_counter_ops and GL_ARB_shader_group_vote add shader intrinsics supported by all desktop vendors to improve functionality and performance GL_KHR_no_error reduces driver overhead by allowing the application to indicate that it expects error-free operation so errors need not be generated In addition to the above features being added to OpenGL 4.6, the following are being released as extensions:
      GL_KHR_parallel_shader_compile allows applications to launch multiple shader compile threads to improve shader compile throughput WGL_ARB_create_context_no_error and GXL_ARB_create_context_no_error allow no error contexts to be created with WGL or GLX that support the GL_KHR_no_error extension “I’m proud to announce OpenGL 4.6 as the most feature-rich version of OpenGL yet. We've brought together the most popular, widely-supported extensions into a new core specification to give OpenGL developers and end users an improved baseline feature set. This includes resolving previous intellectual property roadblocks to bringing anisotropic texture filtering and polygon offset clamping into the core specification to enable widespread implementation and usage,” said Piers Daniell, chair of the OpenGL Working Group at Khronos. “The OpenGL working group will continue to respond to market needs and work with GPU vendors to ensure OpenGL remains a viable and evolving graphics API for all its customers and users across many vital industries.“
      The OpenGL 4.6 specification can be found at https://khronos.org/registry/OpenGL/index_gl.php. The GLSL to SPIR-V compiler glslang has been updated with GLSL 4.60 support, and can be found at https://github.com/KhronosGroup/glslang.
      Sophisticated graphics applications will also benefit from a set of newly released extensions for both OpenGL and OpenGL ES to enable interoperability with Vulkan and Direct3D. These extensions are named:
      GL_EXT_memory_object GL_EXT_memory_object_fd GL_EXT_memory_object_win32 GL_EXT_semaphore GL_EXT_semaphore_fd GL_EXT_semaphore_win32 GL_EXT_win32_keyed_mutex They can be found at: https://khronos.org/registry/OpenGL/index_gl.php
      Industry Support for OpenGL 4.6
      “With OpenGL 4.6 our customers have an improved set of core features available on our full range of OpenGL 4.x capable GPUs. These features provide improved rendering quality, performance and functionality. As the graphics industry’s most popular API, we fully support OpenGL and will continue to work closely with the Khronos Group on the development of new OpenGL specifications and extensions for our customers. NVIDIA has released beta OpenGL 4.6 drivers today at https://developer.nvidia.com/opengl-driver so developers can use these new features right away,” said Bob Pette, vice president, Professional Graphics at NVIDIA.
      "OpenGL 4.6 will be the first OpenGL release where conformant open source implementations based on the Mesa project will be deliverable in a reasonable timeframe after release. The open sourcing of the OpenGL conformance test suite and ongoing work between Khronos and X.org will also allow for non-vendor led open source implementations to achieve conformance in the near future," said David Airlie, senior principal engineer at Red Hat, and developer on Mesa/X.org projects.

      View full story
    • By _OskaR
      Hi,
      I have an OpenGL application but without possibility to wite own shaders.
      I need to perform small VS modification - is possible to do it in an alternative way? Do we have apps or driver modifictions which will catch the shader sent to GPU and override it?
    • By xhcao
      Does sync be needed to read texture content after access texture image in compute shader?
      My simple code is as below,
      glUseProgram(program.get());
      glBindImageTexture(0, texture[0], 0, GL_FALSE, 3, GL_READ_ONLY, GL_R32UI);
      glBindImageTexture(1, texture[1], 0, GL_FALSE, 4, GL_WRITE_ONLY, GL_R32UI);
      glDispatchCompute(1, 1, 1);
      // Does sync be needed here?
      glUseProgram(0);
      glBindFramebuffer(GL_READ_FRAMEBUFFER, framebuffer);
      glFramebufferTexture2D(GL_READ_FRAMEBUFFER, GL_COLOR_ATTACHMENT0,
                                     GL_TEXTURE_CUBE_MAP_POSITIVE_X + face, texture[1], 0);
      glReadPixels(0, 0, kWidth, kHeight, GL_RED_INTEGER, GL_UNSIGNED_INT, outputValues);
       
      Compute shader is very simple, imageLoad content from texture[0], and imageStore content to texture[1]. Does need to sync after dispatchCompute?
  • Advertisement