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--- wiki2:ogl [2015/11/29 18:41]
alfred [glDrawArrays & glDrawElements]
+++ wiki2:ogl [2020/05/09 09:25] (actual)
@@ Línea 25: / Línea 25: @@
   * https://open.gl/depthstencils
   * https://open.gl/framebuffers
+==== VBO (Vertex Buffer Objects) ====
+OpenGL ES defines the concept of buffers for exchanging data between memory areas. A buffer is a contiguous range of RAM that the graphics processor can control and manage. All the data that programs supply to the GPU should be in buffers. It doesn’t matter if a buffer stores geometric data, colors, hints for lighting effects, or other information.
+The process of creating and using VBOs (Vertex Buffer Objects) should be familiar to you because it mimics the process used for textures: first generate a ‘‘name,’’ allocate space for the data, load the data, and then use glBindBuffer() whenever you want to use it.
+  - Generate. ''glGenBuffers()''. Ask OpenGL ES to generate a unique identifier for a buffer that the graphics processor controls.
+  - Bind. ''glBindBuffer()''. Tell OpenGL ES to use a buffer for subsequent operations.
+  - Buffer Data. ''glBufferData() or glBufferSubData()''. Tell OpenGL ES to allocate and initialize sufficient contiguous memory for a currently bound buffer—often by copying data from CPU-controlled memory into the allocated memory.
+  - Enable or Disable. Tell OpenGL ES whether to use data in buffers during subsequent rendering.
+  - Set Pointers. Tell OpenGL ES about the types of data in buffers and any memory offsets needed to access the data.
+  - Draw ''glDrawArrays() or glDrawElements()''. Tell OpenGL ES to render all or part of a scene using data in currently bound and enabled buffers.
+  - Delete''glDeleteBuffers()''. Tell OpenGL ES to delete previously generated buffers and free associated resources.
+<code objc>
+-(void)createVBO {
+	int numXYZElements=3;
+	int numNormalElements=3;
+	int numColorElements=4;
+	int numTextureCoordElements=2;
+	long totalXYZBytes;
+	long totalNormalBytes;
+	long totalTexCoordinateBytes;
+	int numBytesPerVertex;
+	// we need to generate a name for this VBO
+	glGenBuffers(1, &m_VBO_SphereDataName);
+	glBindBuffer(GL_ARRAY_BUFFER,m_VBO_SphereDataName);
+	/*
+	the size of each vertex in the lines 2ff. And in this case a
+	vertex is the summation of its coordinates, texture coordinates, and
+	the normal vector, as required. The total is now multiplied by the total
+	number of vertices.
+	*/
+	numBytesPerVertex=numXYZElements;
+	if(m_UseNormals) numBytesPerVertex+=numNormalElements;
+	if(m_UseTexture) numBytesPerVertex+=numTextureCoordElements;
+	numBytesPerVertex*=sizeof(GLfloat);
+	/*
+	allocates the memory on the GPU. The final parameter is a hint to the
+	driver saying that the data is never expected to change. If you expect
+	to update it, then use GL_DYNAMIC_DRAW.
+	*/
+	glBufferData(GL_ARRAY_BUFFER, numBytesPerVertex*m_NumVertices, 0, GL_STATIC_DRAW);
+	/*
+	Here we use memory mapping by calling glMapBufferOES(). This
+	returns a pointer to a memory-mapped portion of the GPU’s data
+	storage inside the application’s address space. The direct method uses
+	the more traditional glBufferData().
+	*/
+	GLubyte *vboBuffer=(GLubyte *)glMapBufferOES(GL_ARRAY_BUFFER, GL_WRITE_ONLY_OES);
+	/*
+	Now calculate the total number of bytes for each data type.
+	*/
+	totalXYZBytes=numXYZElements*m_NumVertices*sizeof(GLfloat);
+	totalNormalBytes=numNormalElements*m_NumVertices*sizeof(GLfloat);
+	totalTexCoordinateBytes=numTextureCoordElements*m_NumVertices*sizeof(GLfloat);
+	// it is possible to copy the individual buffers one at a time by merely using memcpy()
+	memcpy(vboBuffer,m_VertexData,totalXYZBytes);
+	if(m_UseNormals) {
+		vboBuffer += totalXYZBytes;
+		memcpy(vboBuffer,m_NormalData,totalNormalBytes);
+	}
+	if(m_UseTexture) {
+		vboBuffer += totalNormalBytes;
+		memcpy(vboBuffer,m_TexCoordsData,totalTexCoordinateBytes);
+	}
+	// forces the actual copy action to execute
+	glUnmapBufferOES(GL_ARRAY_BUFFER);
+	m_TotalXYZBytes=totalXYZBytes;
+	m_TotalNormalBytes=totalNormalBytes;
+}
+</code>
+<code objc>
+-(bool)renderVBO {
+	int i;
+	static int counter=0;
+	/*
+	binds it, in the same way a texture is bound. This simply makes
+	it the current object in use, until another is bound or this one is
+	unbound with glBindBuffer(GL_ARRAY_BUFFER, 0);.
+	*/
+	glBindBuffer(GL_ARRAY_BUFFER, m_VBO_SphereDataName);
+	glMatrixMode(GL_MODELVIEW);
+	glDisable(GL_CULL_FACE);
+	glEnable(GL_BLEND);
+	glEnable(GL_DEPTH_TEST);
+	/*
+	enable the various data buffers as has been done in previous
+	execute() methods.
+	*/
+	glEnableClientState(GL_VERTEX_ARRAY);
+	if(m_UseNormals) glEnableClientState(GL_NORMAL_ARRAY);
+	/*
+	When using VBOs, the various pointers to the data blocks are the offset
+	from the first element, which always starts at ‘‘address’’ of zero instead
+	one in the app’s own address space. So, the vertex pointer starts at address
+	of 0, while the normals are right after the vertices, and the texture
+	coordinates are right after the normals.
+	*/
+	glVertexPointer(3,GL_FLOAT,0,(GLvoid*)(char*)0);
+	glNormalPointer(GL_FLOAT,0,(const GLvoid*)(char*)(0+m_TotalXYZBytes));
+	glTexCoordPointer(2,GL_FLOAT,0, (const GLvoid*)((char*)(m_TotalXYZBytes+m_TotalNormalBytes)));
+	if(m_UseTexture) {
+		if(m_TexCoordsData!=nil) {
+			glEnable(GL_TEXTURE_2D);
+			glEnableClientState(GL_TEXTURE_COORD_ARRAY);
+			if(m_TextureID!=0) glBindTexture(GL_TEXTURE_2D, m_TextureID);
+		}
+	} else {
+		glDisableClientState(GL_TEXTURE_COORD_ARRAY);
+	}
+	/*
+	Draw
+	*/
+	glDrawArrays(GL_TRIANGLE_STRIP, 0, (m_Slices+1)*2*(m_Stacks-1)+2);
+	glDisable(GL_BLEND);
+	glDisable(GL_TEXTURE_2D);
+	return true;
+}
+</code>
 ===== Texturas =====
+==== Básico ====
 Creating textures is very similar to creating vertex buffers : Create a texture, bind it, fill it, and configure it.
@@ Línea 48: / Línea 181: @@
 glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
 </code>
+==== Animar texturas ====
+=== Usando el fragment shader ===
+  * {{:wiki2:ogl:animating.textures.zip|}}
+==== Renderizar sobre textura ====
+Para esto se usa un FBO. Básicamente creas el FBO, reemplazas el buffer donde renderizas por el del FBO creado y dibujas, luego enlazas otra vez el buffer por defecto y en el FBO tienes la textura.
+Recuerda indicar el tamaño de píxels, haber creado anteriormente de las texturas que vas a usar en el fbo y tener el shader program activo.
+:!: Recuerda que para OpenGL el 0,0 está en la esquina de abajo a la izquierda. Si el sistema que usas cambia, es probable que **la textura fbo aparezca volteada**.
+  * {{:wiki2:ogl:fbo.zip|}}
+===== Transformaciones =====
+==== Anidar transformaciones (push y pop matrix) ====
+Para anidar transformaciones dentro de otras (al mover, escalar un elemento se mueva y escale igual el que tiene dentro), las figuras hijo aplicarán sus transformaciones a partir de la matriz del modelo de la padre.
+Es decir:
+<code java>
+float[] translateMatrix = new float[16];
+setIdentityM(translateMatrix, 0);
+float[] scaleMatrix = new float[16];
+setIdentityM(scaleMatrix, 0);
+if (mMatrix == null) {
+    // Si no tiene padre inicializamos la matriz del modelo a la identidad
+    setIdentityM(modelMatrix, 0);
+} else {
+    // Si tiene padre usamos su matriz de modelo para aplicar las nuevas transformaciones
+    for (int i = 0; i < 16; i++)
+        modelMatrix[i] = mMatrix[i];
+}
+// Creamos nuestras transformaciones
+translateM(translateMatrix, 0, posX, posY, posZ);
+scaleM(scaleMatrix, 0, sizeX, sizeY, sizeZ);
+float[] temp = new float[16];
+// Aplicamos las transformaciones sobre la matriz del modelo (anterior o identidad)
+multiplyMM(temp, 0, modelMatrix, 0, translateMatrix, 0);
+for (int i = 0; i < 16; i++)
+    modelMatrix[i] = temp[i];
+multiplyMM(temp, 0, modelMatrix, 0, scaleMatrix, 0);
+for (int i = 0; i < 16; i++)
+    modelMatrix[i] = temp[i];
+</code>
+  * {{:wiki2:ogl:nested.transforms.zip|}}
 ===== Lenguaje GLSL =====
@@ Línea 166: / Línea 350: @@
 </code>
 ===== Shaders en general =====
+  * :!: El optimizador de GLSL borrará todas las variables que no uses.
 ===== Vertex Shader =====
 ==== Cambiar el tamaño de los puntos dibujados ====
@@ Línea 177: / Línea 363: @@
 </code>
+==== Hacer el color algo más oscuro ====
+<code>
+gl_FragColor = texture2D(u_TextureUnit, v_TextureCoordinates) * vec4(0.5, 0.5, 0.5, 1);
+</code>
 ===== Otros =====
 ==== Código ejemplo iOS ====

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