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JavierGonz

OpenGL
Editing pixel of a texture

12 posts in this topic

Hello,

 

I'm trying to edit the pixels of a texture in order to create a program like Paint (windows). The idea is that the user can use the mouse to draw in a screen.

 

This is my code, I create an array of pixels and set it with white and red pixels. But when I try to render the texture I can only see a red quad. (It's only rendering one color)

I'm using OpenGL 2.0

for(int y = 0; y < SCREEN_WIDTH; ++y) 
    for(int x = 0; x < SCREEN_HEIGHT; ++x)
    {
        if(x % 2 == 0)
        {
           screenData[y][x][0] = 179;
           screenData[y][x][1] = 53;
           screenData[y][x][2] = 53;
        }
        else
        {
           screenData[y][x][0] = 255;
           screenData[y][x][1] = 255;
           screenData[y][x][2] = 255;
        }
    }
 
glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
//Generate a texture and holds the ID in blackboard
glGenTextures(1, &blackboard);
//Set the current texture in order to modify it
glBindTexture(GL_TEXTURE_2D, blackboard);
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_NEAREST);
 
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, 1280, 720, 0, GL_RGB, GL_UNSIGNED_BYTE, &screenData);
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remove the ampersand infront of 'screenData' at the end of your glTexImage2D call. you're passing in the address of the address of the data, when you just want the address of the data (which is what 'screenData' alone already is)

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Thanks for the replies.

 

The problem is the same after the changes, Just the red color is rendering.

 

// Clear screen
for(int y = 0; y < SCREEN_HEIGHT; ++y) 
for(int x = 0; x < SCREEN_WIDTH; ++x)
{
if(x % 2 == 0)
{
screenData[y][x][0] = 179;
screenData[y][x][1] = 53;
screenData[y][x][2] = 53;
}
else
{
screenData[y][x][0] = 255;
screenData[y][x][1] = 255;
screenData[y][x][2] = 255;
}
}
 
glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
//Generate a texture and holds the ID in blackboard
glGenTextures(1, &blackboard);
//Set the current texture in order to modify it
glBindTexture(GL_TEXTURE_2D, blackboard);
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_NEAREST);
 
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, 1280, 720, 0, GL_RGB, GL_UNSIGNED_BYTE, screenData);
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The problem is probably somewhere else, how are you drawing it? Also, gDebugger is a nice tool to debug opengl programs, I would suggest using it to make sure that the texture is correct.

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Generation of texture co-ordinates may be wrong (not shown in the OP's snippet). Do you use normalized co-ordinates or full size co-ordinates for (u,v)? 

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remove clamp add 

  glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_MODULATE); 

 

but anyway we don't see your drawing routine that might cause trouble.

anyway change your 3d array to 1d (its not so hard)

 

 

and why do you use glPixelStorei(GL_UNPACK_ALIGNMENT, 1);

 

here is how i make texture from pixels:

ofc GLCAM_TEX is unsigned int



glEnable(GL_TEXTURE_2D);
pData = new unsigned int [256*256*3];
glGenTextures(1, &GLCAM_TEX);           //Texture binding
glBindTexture(GL_TEXTURE_2D, GLCAM_TEX);
glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_MODULATE);
glTexImage2D(GL_TEXTURE_2D, 0, 3, 256, 256, 0, GL_RGB, GL_UNSIGNED_BYTE, pData);
  glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
  glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
		  glDisable(GL_TEXTURE_2D);
Edited by ___
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glEnable(GL_TEXTURE_2D);
pData = new unsigned int [256*256*3];
glGenTextures(1, &GLCAM_TEX);           //Texture binding
glBindTexture(GL_TEXTURE_2D, GLCAM_TEX);
glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_MODULATE);
glTexImage2D(GL_TEXTURE_2D, 0, 3, 256, 256, 0, GL_RGB, GL_UNSIGNED_BYTE, pData);
  glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
  glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
		  glDisable(GL_TEXTURE_2D);

 

You should use unsigned char instead of unsigned int, now you're allocating too much memory for the data.

Edited by Sponji
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You might want to also make the second color soomething like green or blue, it might be just blurring them for whatever reason and you dont see the difference because both colors are close to red.

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Here are my drawing routines, and my shaders.

 

Drawing routine:

//We clear the COLOR_BUFFER_BIT, this is the buffer that handle color issues.
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
 
//Set the Vertex Attribute with VertexArray
glVertexAttribPointer(0, 3, GL_FLOAT, false, 0, vertexArray);
glEnableVertexAttribArray(0);
glDrawArrays(GL_TRIANGLE_FAN, 0, 4);
 
// Call IwGL swap instead of egl directly
IwGLSwapBuffers();
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And my shader setup

 

vertexSrc = "attribute vec4 position; attribute vec4 inputTextureCoordinate; varying vec2 textureCoordinate; void main() { gl_Position = position; textureCoordinate = inputTextureCoordinate.xy;}";
fragmentSrc = "varying highp vec2 textureCoordinate; uniform sampler2D videoFrame; precision mediump float; void main() { gl_FragColor = texture2D(videoFrame, textureCoordinate); }";
 
//Position of the triangle (x,y,z) why 4 D:!
//the value is for example, 0.4f is 40% of the glViewPort.
float size = 1.0f;
vertexArray[0]  =  -size; vertexArray[1]  =   size; vertexArray[2]   =  0.0f;
vertexArray[3]  =  -size; vertexArray[4]  =  -size; vertexArray[5]   =  0.0f;
vertexArray[6]  =   size; vertexArray[7]  =  -size; vertexArray[8]   =  0.0f;
vertexArray[9]  =   size; vertexArray[10]  =  size; vertexArray[11]  =  0.0f;
 
// Get dimensions from IwGL
int w = SCREEN_WIDTH;
int h = SCREEN_HEIGHT;
 
//Set the place where we will draw, in this case is a rectangle of wxh with starting position at (0,0).
glViewport(0, 0, w, h) ;
glClearColor(0, 0, 0, 1);

//Create a program to attach vertex and fragments shaders (Source code) to it.
GLuint shaderProgram = glCreateProgram();
//Loading source codes.
GLuint vertexShader = createShader(GL_VERTEX_SHADER, vertexSrc);
GLuint fragmentShader = createShader(GL_FRAGMENT_SHADER, fragmentSrc);
 
//Attach a source code to the whole program (ShaderProgram)
glAttachShader(shaderProgram, vertexShader);
glAttachShader(shaderProgram, fragmentShader);
 
//Set the location of the "position" variable defined before.
//If I remove this, the code works exactly the same way. I think OpenGL set por default
//to 0 the first variable in the code.
glBindAttribLocation(shaderProgram, 0, "position");
 
//Linking phase, create a whole functionally program with all attached shaders.
glLinkProgram(shaderProgram);
 
//It's like executing a .exe in windows.
glUseProgram(shaderProgram);

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Your texture coordinates aren't being passed into the shader. I don't see any texture coordinates.

Edited by radioteeth
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A quad rendering to the screen could very well be one color if there are no texture coordinates involved. If the coordinates are not given, OpenGl will just take the color from one of the corners (its always the same, I just am not sure which one) and makes the whole polygon that.

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