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--- wiki2:oglpipeline [2015/11/20 19:20]
alfred creado
+++ wiki2:oglpipeline [2020/05/09 09:25] (actual)
@@ Línea 1: / Línea 1: @@
 ====== OpenGL Pipeline ======
+===== OpenGL Pipeline Básico =====
+==== Load pixels in memory ====
+=== Android version ===
+<code java>
+float[] tableVerticesWithTriangles = {
+        // Triangle 1
+, 0.5f,
+        -0.5f,  0,
+.5f,  0,
+        // Triangle 2
+, 0,
+.5f, -0.5f,
+        -0.5f,  -0.5f
+};
+vertexData = ByteBuffer
+        .allocateDirect(tableVerticesWithTriangles.length * BYTES_PER_FLOAT)
+        .order(ByteOrder.nativeOrder())
+        .asFloatBuffer();
+vertexData.put(tableVerticesWithTriangles);
+</code>
+==== Change the area where we are gonna render ====
+<code java>
+@Override
+public void onSurfaceChanged(GL10 glUnused, int width, int height) {
+    glViewport(0, 0, width, height);
+}
+</code>
+==== Coding vertex shader ====
+<code java>
+attribute vec4 a_Position;
+void main()
+{
+    gl_Position = a_Position;
+    gl_PointSize = 10.0;
+}
+</code>
+==== Coding fragment shader ====
+<code>
+precision mediump float;
+uniform vec4 u_Color;
+void main()
+{
+    gl_FragColor = u_Color;
+}
+</code>
+==== Compiling shaders ====
+<code java>
+private int compileShader(int type, String shaderCode) {
+    final int shaderObjectId = glCreateShader(type);
+    if (shaderObjectId == 0) {
+        Log.w(TAG, "Could not create new shader.");
+        return 0;
+    }
+    glShaderSource(shaderObjectId, shaderCode);
+    glCompileShader(shaderObjectId);
+    final int[] compileStatus = new int[1];
+    glGetShaderiv(shaderObjectId, GL_COMPILE_STATUS, compileStatus, 0);
+    Log.v(TAG, "Results of compiling source:" + "\n" + shaderCode + "\n:"  + glGetShaderInfoLog(shaderObjectId));
+    if (compileStatus[0] == 0) {
+        glDeleteShader(shaderObjectId);
+        Log.w(TAG, "Compilation of shader failed.");
+        return 0;
+    }
+    Log.w(TAG, "Compilation of shader was good.");
+    return shaderObjectId;
+}
+</code>
+==== Link and use the shader program ====
+<code java>
+public int linkProgram(int vertexShaderId, int fragmentShaderId) {
+    final int programObjectId = glCreateProgram();
+    if (programObjectId == 0) {
+        Log.w(TAG, "Could not create new program");
+        return 0;
+    }
+    glAttachShader(programObjectId, vertexShaderId);
+    glAttachShader(programObjectId, fragmentShaderId);
+    glLinkProgram(programObjectId);
+    final int[] linkStatus = new int[1];
+    glGetProgramiv(programObjectId, GL_LINK_STATUS, linkStatus, 0);
+    Log.v(TAG, "Results of linking program:\n" + glGetProgramInfoLog(programObjectId));
+    if (linkStatus[0] == 0) {
+        glDeleteProgram(programObjectId);
+        Log.w(TAG, "Linking of program failed.");
+        return 0;
+    }
+    glValidateProgram(programObjectId);
+    final int[] validateStatus = new int[1];
+    glGetProgramiv(programObjectId, GL_VALIDATE_STATUS, validateStatus, 0);
+    Log.v(TAG, "Results of validating program: " + validateStatus[0]
+            + "\nLog:" + glGetProgramInfoLog(programObjectId));
+    if (validateStatus[0] == 0) {
+        Log.w(TAG, "Validation program failed.");
+        return 0;
+    }
+    return programObjectId;
+}
+</code>
+==== Initialize values ====
+  * Set the color to clear the screen
+  * Obtain the shaders code in string format
+  * Link and use the shader program
+  * As we are working with fixed triangles, assign shader variable values
+<code java>
+glClearColor(0.0f, 0.0f, 0.0f, 0.0f);
+String vertexShaderSource = Utils.ResourcesReader(context, R.raw.vertex);
+String fragmentShaderSource = Utils.ResourcesReader(context, R.raw.fragment);
+int vertexShader = compileShader(GL_VERTEX_SHADER, vertexShaderSource);
+int fragmentShader = compileShader(GL_FRAGMENT_SHADER, fragmentShaderSource);
+program = linkProgram(vertexShader, fragmentShader);
+glUseProgram(program);
+uColorLocation = glGetUniformLocation(program, U_COLOR);
+aPositionLocation = glGetAttribLocation(program, A_POSITION);
+vertexData.position(0);
+glVertexAttribPointer(aPositionLocation, POSITION_COMPONENT_COUNT, GL_FLOAT,
+        false, 0, vertexData);
+glEnableVertexAttribArray(aPositionLocation);
+</code>
+==== Render ====
+<code java>
+glClear(GL_COLOR_BUFFER_BIT);
+glUniform4f(uColorLocation, 1.0f, 0f, 0f, 1.0f);
+glDrawArrays(GL_TRIANGLES, 0, 3);
+glUniform4f(uColorLocation, 0.0f, 0f, 1f, 1.0f);
+glDrawArrays(GL_TRIANGLES, 3, 3);
+</code>
+==== Functional examples ====
+  * {{:wiki2:ogl:two-triangles.zip|}}
+===== Color =====
+==== Define vertices, color and indexs ====
+<code java>
+float[] tableVerticesWithTriangles = {
+        // x, y          r,g,b
+, 0.5f,         1,0,0,
+        -0.5f,  0,       0,1,0,
+.5f,  0,        0,0,1
+};
+vertexData = ByteBuffer
+        .allocateDirect(tableVerticesWithTriangles.length * BYTES_PER_FLOAT)
+        .order(ByteOrder.nativeOrder())
+        .asFloatBuffer();
+vertexData.put(tableVerticesWithTriangles);
+byte[] tableIndices = {0, 1, 2};
+indexArray =  ByteBuffer.allocateDirect(3).put(tableIndices);
+</code>
+==== Shaders ====
+=== Vertex Shader ===
+<code>
+attribute vec4 a_Position;
+attribute vec4 a_Color;
+varying vec4 v_Color;
+void main()
+{
+    v_Color = a_Color;
+    gl_Position = a_Position;
+}
+</code>
+=== Fragment Shader ===
+<code>
+precision mediump float;
+varying vec4 v_Color;
+void main()
+{
+    gl_FragColor = v_Color;
+}
+</code>
+==== Render ====
+  * Obtain the attributes location for color and position.
+  * Write color and position (in this case this step could be performed only once).
+  * Enable them.
+  * Draw them.
+<code java>
+// next step is really important in java
+vertexData.position(0);
+indexArray.position(0);
+glClear(GL_COLOR_BUFFER_BIT);
+aColorLocation = glGetAttribLocation(program, A_COLOR);
+aPositionLocation = glGetAttribLocation(program, A_POSITION);
+glVertexAttribPointer(aPositionLocation, POSITION_COMPONENT_COUNT, GL_FLOAT,
+        false, STRIDE, vertexData);
+glEnableVertexAttribArray(aPositionLocation);
+vertexData.position(POSITION_COMPONENT_COUNT);
+glVertexAttribPointer(aColorLocation, COLOR_COMPONENT_COUNT, GL_FLOAT,
+        false, STRIDE, vertexData);
+glEnableVertexAttribArray(aColorLocation);
+glDrawElements(GL_TRIANGLES, 3, GL_UNSIGNED_BYTE, indexArray);
+glDisableVertexAttribArray(aPositionLocation);
+glDisableVertexAttribArray(aColorLocation);
+</code>
+=== Constant values ===
+<code java>
+private static final int BYTES_PER_FLOAT = 4;
+private static final int POSITION_COMPONENT_COUNT = 2;
+private static final int COLOR_COMPONENT_COUNT = 3;
+private static final int STRIDE = (POSITION_COMPONENT_COUNT + COLOR_COMPONENT_COUNT) * BYTES_PER_FLOAT;
+</code>
+==== Example ====
+{{:wiki2:ogl:color.zip|Example}}
+===== Transformaciones y proyecciones =====
+  * {{:wiki2:ogl:tutorial_3_matrices.pdf|Explicacion de matrices y proyecciones}}
+  * {{:wiki2:ogl:objectoriented.matrix.zip|Ejemplo de matrices y orientación a objetos en OpenGL ES}}
+===== Texturas =====
+==== Cargar texturas ====
+  - Read the texture.
+  - Bind the texture.
+  - Set filtering: a default must be set, or the texture will be black.
+  - Load the bitmap into the bound texture with ''texImage2D''.
+  - Unbind from the texture with ''glBindTexture(GL_TEXTURE_2D, 0)''.
+<code java>
+public static int loadTexture(Context context, int resourceId) {
+    final int[] textureObjectIds = new int[1];
+    glGenTextures(1, textureObjectIds, 0);
+    if (textureObjectIds[0] == 0) {
+        Log.w(TAG, "Could not generate a new OpenGL texture object.");
+        return 0;
+    }
+    final BitmapFactory.Options options = new BitmapFactory.Options();
+    options.inScaled = false;
+    final Bitmap bitmap = BitmapFactory.decodeResource(context.getResources(), resourceId, options);
+    if (bitmap == null) {
+        Log.w(TAG, "Resource ID " + resourceId + " could not be decoded.");
+        glDeleteTextures(1, textureObjectIds, 0);
+        return 0;
+    }
+    glBindTexture(GL_TEXTURE_2D, textureObjectIds[0]);
+    glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
+    glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
+    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
+    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
+    texImage2D(GL_TEXTURE_2D, 0, bitmap, 0);
+    glBindTexture(GL_TEXTURE_2D, 0);
+    bitmap.recycle();
+    Log.w(TAG, "Texture loaded");
+    return textureObjectIds[0];
+}
+</code>
+Podríamos cargar mipmaps:
+<code java>
+glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR_MIPMAP_LINEAR);
+glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
+glGenerateMipmap(GL_TEXTURE_2D);
+</code>
+==== Shaders ====
+=== Vertex ===
+<code>
+attribute vec4 a_Position;
+attribute vec2 a_TextureCoordinates;
+varying vec2 v_TextureCoordinates;
+void main()
+{
+    v_TextureCoordinates = a_TextureCoordinates;
+    gl_Position = a_Position;
+}
+</code>
+=== Fragment ===
+<code>
+precision mediump float;
+uniform sampler2D u_TextureUnit;
+varying vec2 v_TextureCoordinates;
+void main()
+{
+    gl_FragColor = texture2D(u_TextureUnit, v_TextureCoordinates);
+}
+</code>
+==== When render ====
+<code java>
+vertexData.position(0);
+indexArray.position(0);
+glClear(GL_COLOR_BUFFER_BIT);
+glVertexAttribPointer(aPositionLocation, POSITION_COMPONENT_COUNT, GL_FLOAT,
+        false, STRIDE, vertexData);
+vertexData.position(POSITION_COMPONENT_COUNT);
+glVertexAttribPointer(aTextCoordLocation, TEXTURE_COORDINATES_COMPONENT_COUNT, GL_FLOAT,
+        false, STRIDE, vertexData);
+glEnableVertexAttribArray(aPositionLocation);
+glEnableVertexAttribArray(aTextCoordLocation);
+glActiveTexture(GL_TEXTURE0);
+glBindTexture(GL_TEXTURE_2D, texture);
+glUniform1i(uTextureUnitLocation, 0);
+glDrawElements(GL_TRIANGLES, 3, GL_UNSIGNED_BYTE, indexArray);
+glDisableVertexAttribArray(aPositionLocation);
+glDisableVertexAttribArray(aTextCoordLocation);
+</code>
+Setting these values:
+<code java>
+float[] tableVerticesWithTriangles = {
+        // x, y          s,t
+, 0.5f,         0.5f,0,
+        -0.5f,  0,       0,1,
+.5f,  0,        1,1
+};
+</code>
+And these constants:
+<code java>
+private static final int BYTES_PER_FLOAT = 4;
+private static final int POSITION_COMPONENT_COUNT = 2;
+private static final int TEXTURE_COORDINATES_COMPONENT_COUNT = 2;
+private static final int STRIDE = (POSITION_COMPONENT_COUNT + TEXTURE_COORDINATES_COMPONENT_COUNT) * BYTES_PER_FLOAT;
+</code>
+==== Code ====
+  * {{:wiki2:ogl:textures.zip|}}
+===== Luces =====

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